diff --git a/gtk/deprecated/gtkaction.c b/gtk/deprecated/gtkaction.c
index 03ed26e..dc77bcf 100644
--- a/gtk/deprecated/gtkaction.c
+++ b/gtk/deprecated/gtkaction.c
@@ -1915,7 +1915,7 @@ gtk_action_set_accel_path (GtkAction   *action,
  *
  * Since: 2.6
  *
- * Returns: the accel path for this action, or %NULL
+ * Returns: (nullable): the accel path for this action, or %NULL
  *   if none is set. The returned string is owned by GTK+ 
  *   and must not be freed or modified.
  *
@@ -2060,7 +2060,7 @@ gtk_action_disconnect_accelerator (GtkAction *action)
  * item or the toolbar item it creates, this function returns an
  * instance of that menu.
  *
- * Returns: (transfer none): the menu item provided by the
+ * Returns: (transfer none) (nullable): the menu item provided by the
  *               action, or %NULL.
  *
  * Since: 2.12
diff --git a/gtk/deprecated/gtkactiongroup.c b/gtk/deprecated/gtkactiongroup.c
index a08d18c..4c919e2 100644
--- a/gtk/deprecated/gtkactiongroup.c
+++ b/gtk/deprecated/gtkactiongroup.c
@@ -765,7 +765,7 @@ gtk_action_group_get_visible (GtkActionGroup *action_group)
  *
  * Gets the accelerator group.
  * 
- * Returns: (transfer none): the accelerator group associated with this action
+ * Returns: (transfer none) (nullable): the accelerator group associated with this action
  * group or %NULL if there is none.
  *
  * Since: 3.6
@@ -871,7 +871,7 @@ gtk_action_group_set_accel_group (GtkActionGroup *action_group,
  *
  * Looks up an action in the action group by name.
  *
- * Returns: (transfer none): the action, or %NULL if no action by that name exists
+ * Returns: (transfer none) (nullable): the action, or %NULL if no action by that name exists
  *
  * Since: 2.4
  *
diff --git a/gtk/deprecated/gtkfontsel.c b/gtk/deprecated/gtkfontsel.c
index 7812e75..4961bae 100644
--- a/gtk/deprecated/gtkfontsel.c
+++ b/gtk/deprecated/gtkfontsel.c
@@ -1384,8 +1384,8 @@ gtk_font_selection_get_size (GtkFontSelection *fontsel)
  * “Helvetica Bold Italic 12”. Use pango_font_description_equal()
  * if you want to compare two font descriptions.
  * 
- * Returns: A string with the name of the current font, or %NULL if 
- *     no font is selected. You must free this string with g_free().
+ * Returns: (nullable): A string with the name of the current font, or
+ *     %NULL if no font is selected. You must free this string with g_free().
  *
  * Deprecated: 3.2: Use #GtkFontChooser
  */
@@ -1838,8 +1838,8 @@ gtk_font_selection_dialog_buildable_get_internal_child (GtkBuildable *buildable,
  * to “Helvetica Bold Italic 12”.  Use pango_font_description_equal()
  * if you want to compare two font descriptions.
  * 
- * Returns: A string with the name of the current font, or %NULL if no 
- *     font is selected. You must free this string with g_free().
+ * Returns: (nullable): A string with the name of the current font, or
+ *     %NULL if no font is selected. You must free this string with g_free().
  *
  * Deprecated: 3.2: Use #GtkFontChooserDialog
  */
diff --git a/gtk/deprecated/gtkiconfactory.c b/gtk/deprecated/gtkiconfactory.c
index c1fc370..200c811 100644
--- a/gtk/deprecated/gtkiconfactory.c
+++ b/gtk/deprecated/gtkiconfactory.c
@@ -437,7 +437,7 @@ _gtk_icon_factory_get_default_icons (void)
  * using this function directly, so that themes are taken into
  * account.
  *
- * Returns: (transfer none): a #GtkIconSet, or %NULL
+ * Returns: (transfer none) (nullable): a #GtkIconSet, or %NULL
  *
  * Deprecated: 3.10: Use #GtkIconTheme instead.
  */
diff --git a/gtk/deprecated/gtknumerableicon.c b/gtk/deprecated/gtknumerableicon.c
index 7f63f4d..62ac1c2 100644
--- a/gtk/deprecated/gtknumerableicon.c
+++ b/gtk/deprecated/gtknumerableicon.c
@@ -713,7 +713,7 @@ _gtk_numerable_icon_set_background_icon_size (GtkNumerableIcon *self,
  *
  * Returns the currently displayed label of the icon, or %NULL.
  *
- * Returns: the currently displayed label
+ * Returns: (nullable): the currently displayed label, or %NULL
  *
  * Since: 3.0
  *
@@ -825,7 +825,7 @@ gtk_numerable_icon_set_count (GtkNumerableIcon *self,
  * Returns the #GtkStyleContext used by the icon for theming,
  * or %NULL if there’s none.
  *
- * Returns: (transfer none): a #GtkStyleContext, or %NULL.
+ * Returns: (transfer none) (nullable): a #GtkStyleContext, or %NULL.
  *     This object is internal to GTK+ and should not be unreffed.
  *     Use g_object_ref() if you want to keep it around
  *
@@ -919,7 +919,7 @@ gtk_numerable_icon_set_background_gicon (GtkNumerableIcon *self,
  * %NULL if there’s none. The caller of this function does not own
  * a reference to the returned #GIcon.
  *
- * Returns: (transfer none): a #GIcon, or %NULL
+ * Returns: (transfer none) (nullable): a #GIcon, or %NULL
  *
  * Since: 3.0
  *
@@ -992,7 +992,7 @@ gtk_numerable_icon_set_background_icon_name (GtkNumerableIcon *self,
  * Returns the icon name used as the base background image,
  * or %NULL if there’s none.
  *
- * Returns: an icon name, or %NULL
+ * Returns: (nullable): an icon name, or %NULL
  *
  * Since: 3.0
  *
diff --git a/gtk/deprecated/gtkrc.c b/gtk/deprecated/gtkrc.c
index 93fa01d..126feb6 100644
--- a/gtk/deprecated/gtkrc.c
+++ b/gtk/deprecated/gtkrc.c
@@ -1485,7 +1485,7 @@ gtk_rc_find_pixmap_in_path (GtkSettings  *settings,
  * Searches for a theme engine in the GTK+ search path. This function
  * is not useful for applications and should not be used.
  *
- * Returns: (type filename): The filename, if found (must be
+ * Returns: (type filename) (nullable): The filename, if found (must be
  *   freed with g_free()), otherwise %NULL.
  *
  * Deprecated: 3.0: Use #GtkCssProvider instead.
diff --git a/gtk/deprecated/gtkstatusicon.c b/gtk/deprecated/gtkstatusicon.c
index e384974..caaa84f 100644
--- a/gtk/deprecated/gtkstatusicon.c
+++ b/gtk/deprecated/gtkstatusicon.c
@@ -1907,7 +1907,7 @@ gtk_status_icon_get_storage_type (GtkStatusIcon *status_icon)
  * The caller of this function does not own a reference to the
  * returned pixbuf.
  * 
- * Returns: (transfer none): the displayed pixbuf,
+ * Returns: (transfer none) (nullable): the displayed pixbuf,
  *     or %NULL if the image is empty.
  *
  * Since: 2.10
@@ -1936,7 +1936,7 @@ gtk_status_icon_get_pixbuf (GtkStatusIcon *status_icon)
  * The returned string is owned by the #GtkStatusIcon and should not
  * be freed or modified.
  * 
- * Returns: stock id of the displayed stock icon,
+ * Returns: (nullable): stock id of the displayed stock icon,
  *   or %NULL if the image is empty.
  *
  * Since: 2.10
@@ -1965,7 +1965,7 @@ gtk_status_icon_get_stock (GtkStatusIcon *status_icon)
  * The returned string is owned by the #GtkStatusIcon and should not
  * be freed or modified.
  * 
- * Returns: name of the displayed icon, or %NULL if the image is empty.
+ * Returns: (nullable): name of the displayed icon, or %NULL if the image is empty.
  *
  * Since: 2.10
  *
@@ -1995,7 +1995,7 @@ gtk_status_icon_get_icon_name (GtkStatusIcon *status_icon)
  *
  * If this function fails, @icon is left unchanged;
  *
- * Returns: (transfer none): the displayed icon, or %NULL if the image is empty
+ * Returns: (transfer none) (nullable): the displayed icon, or %NULL if the image is empty
  *
  * Since: 2.14
  *
@@ -2570,7 +2570,7 @@ gtk_status_icon_set_tooltip_text (GtkStatusIcon *status_icon,
  *
  * Gets the contents of the tooltip for @status_icon.
  *
- * Returns: the tooltip text, or %NULL. You should free the
+ * Returns: (nullable): the tooltip text, or %NULL. You should free the
  *   returned string with g_free() when done.
  *
  * Since: 2.16
@@ -2660,7 +2660,7 @@ gtk_status_icon_set_tooltip_markup (GtkStatusIcon *status_icon,
  *
  * Gets the contents of the tooltip for @status_icon.
  *
- * Returns: the tooltip text, or %NULL. You should free the
+ * Returns: (nullable): the tooltip text, or %NULL. You should free the
  *   returned string with g_free() when done.
  *
  * Since: 2.16
diff --git a/gtk/deprecated/gtkstyle.c b/gtk/deprecated/gtkstyle.c
index 2cad590..5abc2ec 100644
--- a/gtk/deprecated/gtkstyle.c
+++ b/gtk/deprecated/gtkstyle.c
@@ -4753,7 +4753,7 @@ gtk_widget_class_path (GtkWidget *widget,
  * the application and should not be modified. The pixbuf should be
  * freed after use with g_object_unref().
  *
- * Returns: (transfer full): a new pixbuf, or %NULL if the
+ * Returns: (transfer full) (nullable): a new pixbuf, or %NULL if the
  *     stock ID wasn’t known
  *
  * Deprecated: 3.0: Use gtk_widget_render_icon_pixbuf() instead.
diff --git a/gtk/deprecated/gtkthemingengine.c b/gtk/deprecated/gtkthemingengine.c
index e26e807..3fcb04e 100644
--- a/gtk/deprecated/gtkthemingengine.c
+++ b/gtk/deprecated/gtkthemingengine.c
@@ -951,7 +951,7 @@ gtk_theming_module_init (GtkThemingModule *module)
  * Loads and initializes a theming engine module from the
  * standard directories.
  *
- * Returns: (transfer none): A theming engine, or %NULL if
+ * Returns: (transfer none) (nullable): A theming engine, or %NULL if
  * the engine @name doesn’t exist.
  *
  * Deprecated: 3.14
@@ -1004,7 +1004,7 @@ gtk_theming_engine_load (const gchar *name)
  *
  * Returns the #GdkScreen to which @engine currently rendering to.
  *
- * Returns: (transfer none): a #GdkScreen, or %NULL.
+ * Returns: (transfer none) (nullable): a #GdkScreen, or %NULL.
  *
  * Deprecated: 3.14
  **/
diff --git a/gtk/deprecated/gtkuimanager.c b/gtk/deprecated/gtkuimanager.c
index 30744fd..780af43 100644
--- a/gtk/deprecated/gtkuimanager.c
+++ b/gtk/deprecated/gtkuimanager.c
@@ -1105,7 +1105,7 @@ gtk_ui_manager_get_accel_group (GtkUIManager *manager)
  * function to some container or explicitly ref them, they will survive the
  * destruction of the ui manager.
  *
- * Returns: (transfer none): the widget found by following the path,
+ * Returns: (transfer none) (nullable): the widget found by following the path,
  *     or %NULL if no widget was found
  *
  * Since: 2.4
@@ -1201,7 +1201,7 @@ gtk_ui_manager_get_toplevels (GtkUIManager         *manager,
  * Looks up an action by following a path. See gtk_ui_manager_get_widget()
  * for more information about paths.
  * 
- * Returns: (transfer none): the action whose proxy widget is found by following the path, 
+ * Returns: (transfer none) (nullable): the action whose proxy widget is found by following the path, 
  *     or %NULL if no widget was found.
  *
  * Since: 2.4
diff --git a/gtk/gtkaccelgroup.c b/gtk/gtkaccelgroup.c
index d4c0440..d63c91b 100644
--- a/gtk/gtkaccelgroup.c
+++ b/gtk/gtkaccelgroup.c
@@ -854,7 +854,7 @@ gtk_accel_group_query (GtkAccelGroup   *accel_group,
  * Finds the #GtkAccelGroup to which @closure is connected;
  * see gtk_accel_group_connect().
  *
- * Returns: (transfer none): the #GtkAccelGroup to which @closure
+ * Returns: (transfer none) (nullable): the #GtkAccelGroup to which @closure
  *     is connected, or %NULL
  */
 GtkAccelGroup*
diff --git a/gtk/gtkaccellabel.c b/gtk/gtkaccellabel.c
index bd2a180..2bb0f6d 100644
--- a/gtk/gtkaccellabel.c
+++ b/gtk/gtkaccellabel.c
@@ -352,7 +352,7 @@ gtk_accel_label_finalize (GObject *object)
  * Fetches the widget monitored by this accelerator label. See
  * gtk_accel_label_set_accel_widget().
  *
- * Returns: (transfer none): the object monitored by the accelerator label, or %NULL.
+ * Returns: (transfer none) (nullable): the object monitored by the accelerator label, or %NULL.
  **/
 GtkWidget*
 gtk_accel_label_get_accel_widget (GtkAccelLabel *accel_label)
diff --git a/gtk/gtkaccessible.c b/gtk/gtkaccessible.c
index e8fe6ca..b554b5e 100644
--- a/gtk/gtkaccessible.c
+++ b/gtk/gtkaccessible.c
@@ -207,7 +207,7 @@ gtk_accessible_set_widget (GtkAccessible *accessible,
  * The returned widget does not have a reference added, so
  * you do not need to unref it.
  *
- * Returns: (transfer none): pointer to the #GtkWidget
+ * Returns: (transfer none) (nullable): pointer to the #GtkWidget
  *     corresponding to the #GtkAccessible, or %NULL.
  *
  * Since: 2.22
diff --git a/gtk/gtkactionable.c b/gtk/gtkactionable.c
index 5e25f41..cb9568e 100644
--- a/gtk/gtkactionable.c
+++ b/gtk/gtkactionable.c
@@ -86,7 +86,7 @@ gtk_actionable_default_init (GtkActionableInterface *iface)
  *
  * See gtk_actionable_set_action_name() for more information.
  *
- * Returns: the action name, or %NULL if none is set
+ * Returns: (nullable): the action name, or %NULL if none is set
  *
  * Since: 3.4
  **/
diff --git a/gtk/gtkactionmuxer.c b/gtk/gtkactionmuxer.c
index 643aeb3..287cc85 100644
--- a/gtk/gtkactionmuxer.c
+++ b/gtk/gtkactionmuxer.c
@@ -768,7 +768,7 @@ gtk_action_muxer_new (void)
  * gtk_action_muxer_get_parent:
  * @muxer: a #GtkActionMuxer
  *
- * Returns: (transfer none): the parent of @muxer, or NULL.
+ * Returns: (transfer none) (nullable): the parent of @muxer, or NULL.
  */
 GtkActionMuxer *
 gtk_action_muxer_get_parent (GtkActionMuxer *muxer)
diff --git a/gtk/gtkappchooser.c b/gtk/gtkappchooser.c
index dae884c..8606a4c 100644
--- a/gtk/gtkappchooser.c
+++ b/gtk/gtkappchooser.c
@@ -109,7 +109,7 @@ gtk_app_chooser_get_content_type (GtkAppChooser *self)
  *
  * Returns the currently selected application.
  *
- * Returns: (transfer full): a #GAppInfo for the currently selected
+ * Returns: (transfer full) (nullable): a #GAppInfo for the currently selected
  *     application, or %NULL if none is selected. Free with g_object_unref()
  *
  * Since: 3.0
diff --git a/gtk/gtkappchooserbutton.c b/gtk/gtkappchooserbutton.c
index dc65d72..7b6dcff 100644
--- a/gtk/gtkappchooserbutton.c
+++ b/gtk/gtkappchooserbutton.c
@@ -973,7 +973,7 @@ gtk_app_chooser_button_set_heading (GtkAppChooserButton *self,
  *
  * Returns the text to display at the top of the dialog.
  *
- * Returns: the text to display at the top of the dialog,
+ * Returns: (nullable): the text to display at the top of the dialog,
  *     or %NULL, in which case a default text is displayed
  */
 const gchar *
diff --git a/gtk/gtkappchooserdialog.c b/gtk/gtkappchooserdialog.c
index c582063..1057b27 100644
--- a/gtk/gtkappchooserdialog.c
+++ b/gtk/gtkappchooserdialog.c
@@ -863,8 +863,8 @@ gtk_app_chooser_dialog_set_heading (GtkAppChooserDialog *self,
  *
  * Returns the text to display at the top of the dialog.
  *
- * Returns: the text to display at the top of the dialog, or %NULL, in which
- *     case a default text is displayed
+ * Returns: (nullable): the text to display at the top of the dialog, or
+ *     %NULL, in which case a default text is displayed
  */
 const gchar *
 gtk_app_chooser_dialog_get_heading (GtkAppChooserDialog *self)
diff --git a/gtk/gtkapplication.c b/gtk/gtkapplication.c
index 0a6e668..7cd8197 100644
--- a/gtk/gtkapplication.c
+++ b/gtk/gtkapplication.c
@@ -1154,7 +1154,7 @@ gtk_application_get_windows (GtkApplication *application)
  *
  * Returns the #GtkApplicationWindow with the given ID.
  *
- * Returns: (transfer none): the window with ID @id, or
+ * Returns: (transfer none) (nullable): the window with ID @id, or
  *   %NULL if there is no window with this ID
  *
  * Since: 3.6
diff --git a/gtk/gtkassistant.c b/gtk/gtkassistant.c
index 2945d53..558d5e6 100644
--- a/gtk/gtkassistant.c
+++ b/gtk/gtkassistant.c
@@ -1686,7 +1686,7 @@ gtk_assistant_get_n_pages (GtkAssistant *assistant)
  *
  * Returns the child widget contained in page number @page_num.
  *
- * Returns: (transfer none): the child widget, or %NULL
+ * Returns: (transfer none) (nullable): the child widget, or %NULL
  *     if @page_num is out of bounds
  *
  * Since: 2.10
@@ -2215,7 +2215,7 @@ gtk_assistant_do_set_page_header_image (GtkAssistant *assistant,
  *
  * Gets the header image for @page.
  *
- * Returns: (transfer none): the header image for @page,
+ * Returns: (transfer none) (nullable): the header image for @page,
  *     or %NULL if there’s no header image for the page
  *
  * Since: 2.10
@@ -2306,7 +2306,7 @@ gtk_assistant_do_set_page_side_image (GtkAssistant *assistant,
  *
  * Gets the side image for @page.
  *
- * Returns: (transfer none): the side image for @page,
+ * Returns: (transfer none) (nullable): the side image for @page,
  *     or %NULL if there’s no side image for the page
  *
  * Since: 2.10
diff --git a/gtk/gtkbindings.c b/gtk/gtkbindings.c
index ac45da2..657f9ac 100644
--- a/gtk/gtkbindings.c
+++ b/gtk/gtkbindings.c
@@ -751,7 +751,7 @@ gtk_binding_set_find_interned (const gchar *set_name)
  * The @set_name can either be a name used for gtk_binding_set_new()
  * or the type name of a class used in gtk_binding_set_by_class().
  *
- * Returns: (transfer none): %NULL or the specified binding set
+ * Returns: (transfer none) (nullable): %NULL or the specified binding set
  */
 GtkBindingSet*
 gtk_binding_set_find (const gchar *set_name)
diff --git a/gtk/gtkbuilder.c b/gtk/gtkbuilder.c
index c074eb5..9c498c4 100644
--- a/gtk/gtkbuilder.c
+++ b/gtk/gtkbuilder.c
@@ -1444,7 +1444,7 @@ gtk_builder_add_objects_from_string (GtkBuilder   *builder,
  * Gets the object named @name. Note that this function does not
  * increment the reference count of the returned object.
  *
- * Returns: (transfer none): the object named @name or %NULL if
+ * Returns: (transfer none) (nullable): the object named @name or %NULL if
  *    it could not be found in the object tree.
  *
  * Since: 2.12
@@ -2517,7 +2517,7 @@ gtk_builder_add_callback_symbols (GtkBuilder  *builder,
  * or for any case that one might be cusomizing signal connections
  * using gtk_builder_connect_signals_full()
  *
- * Returns: The callback symbol in @builder for @callback_name, or %NULL
+ * Returns: (nullable): The callback symbol in @builder for @callback_name, or %NULL
  *
  * Since: 3.10
  */
@@ -2660,7 +2660,7 @@ gtk_builder_set_application (GtkBuilder     *builder,
  * g_application_get_default(). If you want to use another application
  * for constructing proxies, use gtk_builder_set_application().
  *
- * Returns: (transfer none): the application being used by the builder,
+ * Returns: (transfer none) (nullable): the application being used by the builder,
  *     or %NULL
  *
  * Since: 3.10
diff --git a/gtk/gtkbutton.c b/gtk/gtkbutton.c
index 315a11b..f9cb6e2 100644
--- a/gtk/gtkbutton.c
+++ b/gtk/gtkbutton.c
@@ -2672,7 +2672,7 @@ gtk_button_set_image (GtkButton *button,
  * This may have been explicitly set by gtk_button_set_image()
  * or constructed by gtk_button_new_from_stock().
  *
- * Returns: (transfer none): a #GtkWidget or %NULL in case there is no image
+ * Returns: (transfer none) (nullable): a #GtkWidget or %NULL in case there is no image
  *
  * Since: 2.6
  */
@@ -2799,7 +2799,7 @@ gtk_button_get_always_show_image (GtkButton *button)
  * Returns the button’s event window if it is realized, %NULL otherwise.
  * This function should be rarely needed.
  *
- * Returns: (transfer none): @button’s event window.
+ * Returns: (transfer none) (nullable): @button’s event window, or %NULL.
  *
  * Since: 2.22
  */
diff --git a/gtk/gtkcalendar.h b/gtk/gtkcalendar.h
index ad4efcd..b9d07e9 100644
--- a/gtk/gtkcalendar.h
+++ b/gtk/gtkcalendar.h
@@ -86,7 +86,7 @@ typedef enum
  *
  * Since: 2.14
  *
- * Returns: Newly allocated string with Pango markup with details
+ * Returns: (nullable): Newly allocated string with Pango markup with details
  * for the specified day, or %NULL.
  */
 typedef gchar* (*GtkCalendarDetailFunc) (GtkCalendar *calendar,
diff --git a/gtk/gtkcellarea.c b/gtk/gtkcellarea.c
index c7b9f2d..0e063b0 100644
--- a/gtk/gtkcellarea.c
+++ b/gtk/gtkcellarea.c
@@ -2450,7 +2450,7 @@ gtk_cell_area_class_install_cell_property (GtkCellAreaClass   *aclass,
  *
  * Finds a cell property of a cell area class by name.
  *
- * Returns: (transfer none): the #GParamSpec of the child property
+ * Returns: (transfer none) (nullable): the #GParamSpec of the child property
  *   or %NULL if @aclass has no child property with that name.
  *
  * Since: 3.0
@@ -3187,7 +3187,7 @@ gtk_cell_area_get_focus_siblings (GtkCellArea     *area,
  * then chose to activate the focus cell for which the event
  * cell may have been a sibling.
  *
- * Returns: (transfer none): the #GtkCellRenderer for which @renderer
+ * Returns: (transfer none) (nullable): the #GtkCellRenderer for which @renderer
  *    is a sibling, or %NULL.
  *
  * Since: 3.0
diff --git a/gtk/gtkcellrenderer.c b/gtk/gtkcellrenderer.c
index 2f157b2..ad51bd5 100644
--- a/gtk/gtkcellrenderer.c
+++ b/gtk/gtkcellrenderer.c
@@ -893,7 +893,7 @@ gtk_cell_renderer_activate (GtkCellRenderer      *cell,
  *
  * Passes an activate event to the cell renderer for possible processing.
  *
- * Returns: (transfer none): A new #GtkCellEditable, or %NULL
+ * Returns: (transfer none) (nullable): A new #GtkCellEditable, or %NULL
  **/
 GtkCellEditable *
 gtk_cell_renderer_start_editing (GtkCellRenderer      *cell,
diff --git a/gtk/gtkcellview.c b/gtk/gtkcellview.c
index 190f895..7f7ecde 100644
--- a/gtk/gtkcellview.c
+++ b/gtk/gtkcellview.c
@@ -1215,7 +1215,7 @@ gtk_cell_view_set_model (GtkCellView  *cell_view,
  * Returns the model for @cell_view. If no model is used %NULL is
  * returned.
  *
- * Returns: (transfer none): a #GtkTreeModel used or %NULL
+ * Returns: (transfer none) (nullable): a #GtkTreeModel used or %NULL
  *
  * Since: 2.16
  **/
@@ -1272,7 +1272,7 @@ gtk_cell_view_set_displayed_row (GtkCellView *cell_view,
  * displayed row. If no row is currently displayed, 
  * %NULL is returned.
  *
- * Returns: the currently displayed row or %NULL
+ * Returns: (nullable): the currently displayed row or %NULL
  *
  * Since: 2.6
  */
diff --git a/gtk/gtkclipboard.c b/gtk/gtkclipboard.c
index 2b0f99c..6647ad5 100644
--- a/gtk/gtkclipboard.c
+++ b/gtk/gtkclipboard.c
@@ -737,7 +737,7 @@ gtk_clipboard_set_with_owner (GtkClipboard          *clipboard,
  * gtk_clipboard_clear() has not subsequently called, returns the owner set
  * by gtk_clipboard_set_with_owner().
  *
- * Returns: (transfer none): the owner of the clipboard, if any;
+ * Returns: (transfer none) (nullable): the owner of the clipboard, if any;
  *     otherwise %NULL.
  **/
 GObject *
diff --git a/gtk/gtkcomboboxtext.c b/gtk/gtkcomboboxtext.c
index a465d8b..503c6b0 100644
--- a/gtk/gtkcomboboxtext.c
+++ b/gtk/gtkcomboboxtext.c
@@ -585,8 +585,8 @@ gtk_combo_box_text_remove_all (GtkComboBoxText *combo_box)
  * function will return its contents (which will not necessarily
  * be an item from the list).
  *
- * Returns: (transfer full): a newly allocated string containing the
- *     currently active text. Must be freed with g_free().
+ * Returns: (transfer full) (nullable): a newly allocated string containing the
+ *     currently active text, or %NULL. Must be freed with g_free().
  *
  * Since: 2.24
  */
diff --git a/gtk/gtkcontainer.c b/gtk/gtkcontainer.c
index 3122bd6..d072b08 100644
--- a/gtk/gtkcontainer.c
+++ b/gtk/gtkcontainer.c
@@ -2465,7 +2465,7 @@ gtk_container_set_focus_child (GtkContainer *container,
  * currently focused widget. That can be obtained by calling
  * gtk_window_get_focus().
  *
- * Returns: (transfer none): The child widget which will receive the
+ * Returns: (transfer none) (nullable): The child widget which will receive the
  *          focus inside @container when the @conatiner is focussed,
  *          or %NULL if none is set.
  *
@@ -3463,7 +3463,7 @@ gtk_container_set_focus_vadjustment (GtkContainer  *container,
  * Retrieves the vertical focus adjustment for the container. See
  * gtk_container_set_focus_vadjustment().
  *
- * Returns: (transfer none): the vertical focus adjustment, or %NULL if
+ * Returns: (transfer none) (nullable): the vertical focus adjustment, or %NULL if
  *   none has been set.
  **/
 GtkAdjustment *
@@ -3518,7 +3518,7 @@ gtk_container_set_focus_hadjustment (GtkContainer  *container,
  * Retrieves the horizontal focus adjustment for the container. See
  * gtk_container_set_focus_hadjustment ().
  *
- * Returns: (transfer none): the horizontal focus adjustment, or %NULL if
+ * Returns: (transfer none) (nullable): the horizontal focus adjustment, or %NULL if
  *   none has been set.
  **/
 GtkAdjustment *
diff --git a/gtk/gtkcsssection.c b/gtk/gtkcsssection.c
index 5de9728..20be38e 100644
--- a/gtk/gtkcsssection.c
+++ b/gtk/gtkcsssection.c
@@ -196,7 +196,7 @@ gtk_css_section_get_parent (const GtkCssSection *section)
  * for example because the CSS was loaded via
  * @gtk_css_provider_load_from_data(), then %NULL is returned.
  *
- * Returns: (transfer none): the #GFile that @section was parsed from
+ * Returns: (transfer none) (nullable): the #GFile that @section was parsed from
  *     or %NULL if @section was parsed from other data
  *
  * Since: 3.2
diff --git a/gtk/gtkdialog.c b/gtk/gtkdialog.c
index e2713b2..8778b5b 100644
--- a/gtk/gtkdialog.c
+++ b/gtk/gtkdialog.c
@@ -1425,7 +1425,7 @@ gtk_dialog_run (GtkDialog *dialog)
  * Gets the widget button that uses the given response ID in the action area
  * of a dialog.
  *
- * Returns: (transfer none): the @widget button that uses the given
+ * Returns: (transfer none) (nullable): the @widget button that uses the given
  *     @response_id, or %NULL.
  *
  * Since: 2.20
diff --git a/gtk/gtkdnd.c b/gtk/gtkdnd.c
index eba82c9..0f8f140 100644
--- a/gtk/gtkdnd.c
+++ b/gtk/gtkdnd.c
@@ -905,7 +905,7 @@ gtk_drag_get_data (GtkWidget      *widget,
  *
  * Determines the source widget for a drag.
  *
- * Returns: (transfer none): if the drag is occurring
+ * Returns: (transfer none) (nullable): if the drag is occurring
  *     within a single application, a pointer to the source widget.
  *     Otherwise, %NULL.
  */
@@ -1202,7 +1202,7 @@ gtk_drag_dest_unset (GtkWidget *widget)
  * Returns the list of targets this widget can accept from
  * drag-and-drop.
  * 
- * Returns: (transfer none): the #GtkTargetList, or %NULL if none
+ * Returns: (transfer none) (nullable): the #GtkTargetList, or %NULL if none
  */
 GtkTargetList*
 gtk_drag_dest_get_target_list (GtkWidget *widget)
diff --git a/gtk/gtkdragsource.c b/gtk/gtkdragsource.c
index 6713b99..1fc2f37 100644
--- a/gtk/gtkdragsource.c
+++ b/gtk/gtkdragsource.c
@@ -214,7 +214,7 @@ gtk_drag_source_unset (GtkWidget *widget)
  * Gets the list of targets this widget can provide for
  * drag-and-drop.
  *
- * Returns: (transfer none): the #GtkTargetList, or %NULL if none
+ * Returns: (transfer none) (nullable): the #GtkTargetList, or %NULL if none
  *
  * Since: 2.4
  */
diff --git a/gtk/gtkentry.c b/gtk/gtkentry.c
index 31f0eff..d0a8de4 100644
--- a/gtk/gtkentry.c
+++ b/gtk/gtkentry.c
@@ -8932,7 +8932,7 @@ gtk_entry_get_icon_gicon (GtkEntry             *entry,
  * no icon or if the icon was set by some other method (e.g., by
  * pixbuf, icon name or gicon).
  *
- * Returns: A stock id, or %NULL if no icon is set or if the icon
+ * Returns: (nullable): A stock id, or %NULL if no icon is set or if the icon
  *          wasn’t set from a stock id
  *
  * Since: 2.16
diff --git a/gtk/gtkentrycompletion.c b/gtk/gtkentrycompletion.c
index 8026806..457e888 100644
--- a/gtk/gtkentrycompletion.c
+++ b/gtk/gtkentrycompletion.c
@@ -1172,7 +1172,7 @@ gtk_entry_completion_set_model (GtkEntryCompletion *completion,
  * Returns the model the #GtkEntryCompletion is using as data source.
  * Returns %NULL if the model is unset.
  *
- * Returns: (transfer none): A #GtkTreeModel, or %NULL if none
+ * Returns: (transfer none) (nullable): A #GtkTreeModel, or %NULL if none
  *     is currently being used
  *
  * Since: 2.4
@@ -1725,7 +1725,7 @@ gtk_entry_completion_cursor_on_match (GtkEntryCompletion *completion,
  * Note that a text column must have been set for this function to work,
  * see gtk_entry_completion_set_text_column() for details. 
  *
- * Returns: (transfer full): The common prefix all rows starting with @key
+ * Returns: (transfer full) (nullable): The common prefix all rows starting with @key
  *   or %NULL if no row matches @key.
  *
  * Since: 3.4
diff --git a/gtk/gtkexpander.c b/gtk/gtkexpander.c
index 6898888..8b97d4e 100644
--- a/gtk/gtkexpander.c
+++ b/gtk/gtkexpander.c
@@ -1962,7 +1962,7 @@ gtk_expander_set_label_widget (GtkExpander *expander,
  * Retrieves the label widget for the frame. See
  * gtk_expander_set_label_widget().
  *
- * Returns: (transfer none): the label widget,
+ * Returns: (transfer none) (nullable): the label widget,
  *     or %NULL if there is none
  *
  * Since: 2.4
diff --git a/gtk/gtkfilechooser.c b/gtk/gtkfilechooser.c
index 5ed25fd..e9ef0fb 100644
--- a/gtk/gtkfilechooser.c
+++ b/gtk/gtkfilechooser.c
@@ -673,7 +673,7 @@ gtk_file_chooser_get_create_folders (GtkFileChooser *chooser)
  * If the file chooser is in folder mode, this function returns the selected
  * folder.
  * 
- * Returns: (type filename): The currently selected filename, or %NULL
+ * Returns: (type filename) (nullable): The currently selected filename, or %NULL
  *  if no file is selected, or the selected file can't
  *  be represented with a local filename. Free with g_free().
  *
@@ -927,7 +927,7 @@ gtk_file_chooser_set_current_folder (GtkFileChooser *chooser,
  * currently-selected folder in that mode, use gtk_file_chooser_get_uri() as the
  * usual way to get the selection.
  * 
- * Returns: (type filename): the full path of the current folder,
+ * Returns: (type filename) (nullable): the full path of the current folder,
  * or %NULL if the current path cannot be represented as a local
  * filename.  Free with g_free().  This function will also return
  * %NULL if the file chooser was unable to load the last folder that
@@ -1021,10 +1021,10 @@ gtk_file_chooser_get_current_name (GtkFileChooser *chooser)
  * If the file chooser is in folder mode, this function returns the selected
  * folder.
  * 
- * Returns: The currently selected URI, or %NULL
- *  if no file is selected. If gtk_file_chooser_set_local_only() is set to %TRUE
- * (the default) a local URI will be returned for any FUSE locations.
- * Free with g_free()
+ * Returns: (nullable): The currently selected URI, or %NULL
+ *     if no file is selected. If gtk_file_chooser_set_local_only() is set to %TRUE
+ *     (the default) a local URI will be returned for any FUSE locations.
+ *     Free with g_free()
  *
  * Since: 2.4
  **/
@@ -1272,8 +1272,8 @@ gtk_file_chooser_set_current_folder_uri (GtkFileChooser *chooser,
  * currently-selected folder in that mode, use gtk_file_chooser_get_uri() as the
  * usual way to get the selection.
  * 
- * Returns: the URI for the current folder.  Free with g_free().  This
- * function will also return %NULL if the file chooser was unable to load the
+ * Returns: (nullable): the URI for the current folder.  Free with g_free().
+ * This function will also return %NULL if the file chooser was unable to load the
  * last folder that was requested from it; for example, as would be for calling
  * gtk_file_chooser_set_current_folder_uri() on a nonexistent folder.
  *
@@ -1560,7 +1560,7 @@ gtk_file_chooser_set_preview_widget (GtkFileChooser *chooser,
  * Gets the current preview widget; see
  * gtk_file_chooser_set_preview_widget().
  *
- * Returns: (transfer none): the current preview widget, or %NULL
+ * Returns: (transfer none) (nullable): the current preview widget, or %NULL
  *
  * Since: 2.4
  **/
@@ -1682,7 +1682,7 @@ gtk_file_chooser_get_use_preview_label (GtkFileChooser *chooser)
  * Gets the #GFile that should be previewed in a custom preview
  * Internal function, see gtk_file_chooser_get_preview_uri().
  *
- * Returns: (transfer full): the #GFile for the file to preview,
+ * Returns: (transfer full) (nullable): the #GFile for the file to preview,
  *     or %NULL if no file is selected. Free with g_object_unref().
  *
  * Since: 2.14
@@ -1752,7 +1752,7 @@ _gtk_file_chooser_remove_shortcut_folder (GtkFileChooser  *chooser,
  * Gets the filename that should be previewed in a custom preview
  * widget. See gtk_file_chooser_set_preview_widget().
  * 
- * Returns: (type filename): the filename to preview, or %NULL if
+ * Returns: (type filename) (nullable): the filename to preview, or %NULL if
  *  no file is selected, or if the selected file cannot be represented
  *  as a local filename. Free with g_free()
  *
@@ -1783,7 +1783,7 @@ gtk_file_chooser_get_preview_filename (GtkFileChooser *chooser)
  * Gets the URI that should be previewed in a custom preview
  * widget. See gtk_file_chooser_set_preview_widget().
  * 
- * Returns: the URI for the file to preview, or %NULL if no file is
+ * Returns: (nullable): the URI for the file to preview, or %NULL if no file is
  * selected. Free with g_free().
  *
  * Since: 2.4
@@ -1831,7 +1831,7 @@ gtk_file_chooser_set_extra_widget (GtkFileChooser *chooser,
  * Gets the current preview widget; see
  * gtk_file_chooser_set_extra_widget().
  *
- * Returns: (transfer none): the current extra widget, or %NULL
+ * Returns: (transfer none) (nullable): the current extra widget, or %NULL
  *
  * Since: 2.4
  **/
@@ -1947,7 +1947,7 @@ gtk_file_chooser_set_filter (GtkFileChooser *chooser,
  *
  * Gets the current filter; see gtk_file_chooser_set_filter().
  *
- * Returns: (transfer none): the current filter, or %NULL
+ * Returns: (transfer none) (nullable): the current filter, or %NULL
  *
  * Since: 2.4
  **/
diff --git a/gtk/gtkfilechoosernative.c b/gtk/gtkfilechoosernative.c
index c43e86f..10c1899 100644
--- a/gtk/gtkfilechoosernative.c
+++ b/gtk/gtkfilechoosernative.c
@@ -199,7 +199,7 @@ G_DEFINE_TYPE_WITH_CODE (GtkFileChooserNative, gtk_file_chooser_native, GTK_TYPE
  *
  * Retrieves the custom label text for the accept button.
  *
- * Returns: The custom label, or %NULL for the default. This string is
+ * Returns: (nullable): The custom label, or %NULL for the default. This string is
  * owned by GTK+ and should not be modified or freed
  *
  * Since: 3.20
@@ -245,7 +245,7 @@ gtk_file_chooser_native_set_accept_label (GtkFileChooserNative *self,
  *
  * Retrieves the custom label text for the cancel button.
  *
- * Returns: The custom label, or %NULL for the default. This string is
+ * Returns: (nullable): The custom label, or %NULL for the default. This string is
  * owned by GTK+ and should not be modified or freed
  *
  * Since: 3.20
diff --git a/gtk/gtkfilefilter.c b/gtk/gtkfilefilter.c
index 43cd05f..c4751e2 100644
--- a/gtk/gtkfilefilter.c
+++ b/gtk/gtkfilefilter.c
@@ -432,7 +432,7 @@ gtk_file_filter_set_name (GtkFileFilter *filter,
  * 
  * Gets the human-readable name for the filter. See gtk_file_filter_set_name().
  * 
- * Returns: The human-readable name of the filter,
+ * Returns: (nullable): The human-readable name of the filter,
  *   or %NULL. This value is owned by GTK+ and must not
  *   be modified or freed.
  * 
diff --git a/gtk/gtkfilesystemmodel.c b/gtk/gtkfilesystemmodel.c
index 32e2cac..62e8d04 100644
--- a/gtk/gtkfilesystemmodel.c
+++ b/gtk/gtkfilesystemmodel.c
@@ -1709,8 +1709,8 @@ _gtk_file_system_model_get_file (GtkFileSystemModel *model,
  * the value and spend a considerable amount of time in iterator 
  * lookups. Both of which are slow.
  *
- * Returns: a pointer to the actual value as stored in @model or %NULL
- *          if no value available yet.
+ * Returns: (nullable): a pointer to the actual value as stored in @model, or %NULL
+ *                      if no value available yet.
  **/
 const GValue *
 _gtk_file_system_model_get_value (GtkFileSystemModel *model,
diff --git a/gtk/gtkfontchooser.c b/gtk/gtkfontchooser.c
index 0b2b514..ff65b69 100644
--- a/gtk/gtkfontchooser.c
+++ b/gtk/gtkfontchooser.c
@@ -135,7 +135,7 @@ gtk_font_chooser_default_init (GtkFontChooserInterface *iface)
  *
  * If the selected font is not installed, returns %NULL.
  *
- * Returns: (transfer none): A #PangoFontFamily representing the
+ * Returns: (transfer none) (nullable): A #PangoFontFamily representing the
  *     selected font family, or %NULL. The returned object is owned by @fontchooser
  *     and must not be modified or freed.
  *
@@ -158,7 +158,7 @@ gtk_font_chooser_get_font_family (GtkFontChooser *fontchooser)
  *
  * If the selected font is not installed, returns %NULL.
  *
- * Returns: (transfer none): A #PangoFontFace representing the
+ * Returns: (transfer none) (nullable): A #PangoFontFace representing the
  *     selected font group details, or %NULL. The returned object is owned by
  *     @fontchooser and must not be modified or freed.
  *
@@ -206,8 +206,8 @@ gtk_font_chooser_get_font_size (GtkFontChooser *fontchooser)
  * Use pango_font_description_equal() if you want to compare two
  * font descriptions.
  *
- * Returns: (transfer full) (allow-none): A string with the name
- *     of the current font, or %NULL if  no font is selected. You must
+ * Returns: (transfer full) (nullable): A string with the name
+ *     of the current font, or %NULL if no font is selected. You must
  *     free this string with g_free().
  *
  * Since: 3.2
@@ -259,7 +259,7 @@ gtk_font_chooser_set_font (GtkFontChooser *fontchooser,
  * Use pango_font_description_equal() if you want to compare two
  * font descriptions.
  *
- * Returns: (transfer full) (allow-none): A #PangoFontDescription for the
+ * Returns: (transfer full) (nullable): A #PangoFontDescription for the
  *     current font, or %NULL if  no font is selected.
  *
  * Since: 3.2
@@ -465,7 +465,7 @@ gtk_font_chooser_set_font_map (GtkFontChooser *fontchooser,
  * Gets the custom font map of this font chooser widget,
  * or %NULL if it does not have one.
  *
- * Returns: (transfer full) (allow-none): a #PangoFontMap, or %NULL
+ * Returns: (transfer full) (nullable): a #PangoFontMap, or %NULL
  *
  * Since: 3.18
  */
diff --git a/gtk/gtkframe.c b/gtk/gtkframe.c
index a875e58..a95bd13 100644
--- a/gtk/gtkframe.c
+++ b/gtk/gtkframe.c
@@ -407,10 +407,10 @@ gtk_frame_set_label (GtkFrame *frame,
  * for the label widget if a non-%NULL argument was passed
  * to gtk_frame_new().)
  * 
- * Returns: the text in the label, or %NULL if there
- *               was no label widget or the lable widget was not
- *               a #GtkLabel. This string is owned by GTK+ and
- *               must not be modified or freed.
+ * Returns: (nullable): the text in the label, or %NULL if there
+ *                      was no label widget or the lable widget was not
+ *                      a #GtkLabel. This string is owned by GTK+ and
+ *                      must not be modified or freed.
  **/
 const gchar *
 gtk_frame_get_label (GtkFrame *frame)
diff --git a/gtk/gtkgesture.c b/gtk/gtkgesture.c
index 9da7654..a3d8775 100644
--- a/gtk/gtkgesture.c
+++ b/gtk/gtkgesture.c
@@ -1015,7 +1015,7 @@ gtk_gesture_init (GtkGesture *gesture)
  * Returns the master #GdkDevice that is currently operating
  * on @gesture, or %NULL if the gesture is not being interacted.
  *
- * Returns: (transfer none) (allow-none): a #GdkDevice, or %NULL
+ * Returns: (transfer none) (nullable): a #GdkDevice, or %NULL
  *
  * Since: 3.14
  **/
@@ -1568,7 +1568,7 @@ _gtk_gesture_cancel_sequence (GtkGesture       *gesture,
  * handled by @gesture. See gtk_gesture_set_window() for more
  * information.
  *
- * Returns: (transfer none) (allow-none): the user defined window, or %NULL if none
+ * Returns: (transfer none) (nullable): the user defined window, or %NULL if none
  *
  * Since: 3.14
  **/
diff --git a/gtk/gtkglarea.c b/gtk/gtkglarea.c
index 4098409..e18a3e8 100644
--- a/gtk/gtkglarea.c
+++ b/gtk/gtkglarea.c
@@ -998,7 +998,7 @@ gtk_gl_area_set_error (GtkGLArea    *area,
  *
  * Gets the current error set on the @area.
  *
- * Returns: (transfer none): the #GError or %NULL
+ * Returns: (transfer none) (nullable): the #GError, or %NULL
  *
  * Since: 3.16
  */
diff --git a/gtk/gtkheaderbar.c b/gtk/gtkheaderbar.c
index d0779bd..827abe0 100644
--- a/gtk/gtkheaderbar.c
+++ b/gtk/gtkheaderbar.c
@@ -1218,7 +1218,7 @@ gtk_header_bar_set_title (GtkHeaderBar *bar,
  *
  * Retrieves the title of the header. See gtk_header_bar_set_title().
  *
- * Returns: the title of the header, or %NULL if none has
+ * Returns: (nullable): the title of the header, or %NULL if none has
  *    been set explicitly. The returned string is owned by the widget
  *    and must not be modified or freed.
  *
@@ -1279,7 +1279,7 @@ gtk_header_bar_set_subtitle (GtkHeaderBar *bar,
  *
  * Retrieves the subtitle of the header. See gtk_header_bar_set_subtitle().
  *
- * Returns: the subtitle of the header, or %NULL if none has
+ * Returns: (nullable): the subtitle of the header, or %NULL if none has
  *    been set explicitly. The returned string is owned by the widget
  *    and must not be modified or freed.
  *
@@ -1372,7 +1372,7 @@ gtk_header_bar_set_custom_title (GtkHeaderBar *bar,
  * Retrieves the custom title widget of the header. See
  * gtk_header_bar_set_custom_title().
  *
- * Returns: (transfer none): the custom title widget
+ * Returns: (transfer none) (nullable): the custom title widget
  *    of the header, or %NULL if none has been set explicitly.
  *
  * Since: 3.10
diff --git a/gtk/gtkicontheme.c b/gtk/gtkicontheme.c
index e425169..4c90a37 100644
--- a/gtk/gtkicontheme.c
+++ b/gtk/gtkicontheme.c
@@ -3624,7 +3624,7 @@ gtk_icon_info_get_base_scale (GtkIconInfo *icon_info)
  * filename if a builtin icon is returned; in this case, you should
  * use gtk_icon_info_get_builtin_pixbuf().
  * 
- * Returns: (type filename): the filename for the icon, or %NULL
+ * Returns: (type filename): (nullable): the filename for the icon, or %NULL
  *     if gtk_icon_info_get_builtin_pixbuf() should be used instead.
  *     The return value is owned by GTK+ and should not be modified
  *     or freed.
@@ -3647,7 +3647,7 @@ gtk_icon_info_get_filename (GtkIconInfo *icon_info)
  * built in icon images, you must pass the %GTK_ICON_LOOKUP_USE_BUILTIN
  * to gtk_icon_theme_lookup_icon().
  *
- * Returns: (transfer none): the built-in image pixbuf, or %NULL.
+ * Returns: (transfer none): (nullable): the built-in image pixbuf, or %NULL.
  *     No extra reference is added to the returned pixbuf, so if
  *     you want to keep it around, you must use g_object_ref().
  *     The returned image must not be modified.
@@ -5219,7 +5219,7 @@ gtk_icon_info_get_attach_points (GtkIconInfo  *icon_info,
  * 
  * This function is deprecated and always returns %NULL.
  * 
- * Returns: %NULL
+ * Returns: (nullable): %NULL
  *
  * Since: 2.4
  *
diff --git a/gtk/gtkiconview.c b/gtk/gtkiconview.c
index e134053..a404d0d 100644
--- a/gtk/gtkiconview.c
+++ b/gtk/gtkiconview.c
@@ -4441,7 +4441,7 @@ gtk_icon_view_convert_widget_to_bin_window_coords (GtkIconView *icon_view,
  * See gtk_icon_view_convert_widget_to_bin_window_coords() for converting
  * widget coordinates to bin_window coordinates.
  * 
- * Returns: The #GtkTreePath corresponding to the icon or %NULL
+ * Returns: (nullable): The #GtkTreePath corresponding to the icon or %NULL
  * if no icon exists at that position.
  *
  * Since: 2.6 
@@ -5082,7 +5082,7 @@ gtk_icon_view_set_model (GtkIconView *icon_view,
  * Returns the model the #GtkIconView is based on.  Returns %NULL if the
  * model is unset.
  *
- * Returns: (transfer none): A #GtkTreeModel, or %NULL if none is
+ * Returns: (transfer none) (nullable): A #GtkTreeModel, or %NULL if none is
  *     currently being used.
  *
  * Since: 2.6 
diff --git a/gtk/gtkimage.c b/gtk/gtkimage.c
index 7494f41..2e731fa 100644
--- a/gtk/gtkimage.c
+++ b/gtk/gtkimage.c
@@ -1325,7 +1325,7 @@ gtk_image_get_storage_type (GtkImage *image)
  * The caller of this function does not own a reference to the
  * returned pixbuf.
  * 
- * Returns: (transfer none): the displayed pixbuf, or %NULL if
+ * Returns: (transfer none) (nullable): the displayed pixbuf, or %NULL if
  * the image is empty
  **/
 GdkPixbuf*
@@ -1412,7 +1412,7 @@ gtk_image_get_icon_set  (GtkImage        *image,
  * The caller of this function does not own a reference to the
  * returned animation.
  * 
- * Returns: (transfer none): the displayed animation, or %NULL if
+ * Returns: (transfer none) (nullable): the displayed animation, or %NULL if
  * the image is empty
  **/
 GdkPixbufAnimation*
diff --git a/gtk/gtklabel.c b/gtk/gtklabel.c
index fd1adf3..859b56c 100644
--- a/gtk/gtklabel.c
+++ b/gtk/gtklabel.c
@@ -2075,7 +2075,7 @@ gtk_label_set_mnemonic_widget (GtkLabel  *label,
  * Retrieves the target of the mnemonic (keyboard shortcut) of this
  * label. See gtk_label_set_mnemonic_widget().
  *
- * Returns: (transfer none): the target of the label’s mnemonic,
+ * Returns: (transfer none) (nullable): the target of the label’s mnemonic,
  *     or %NULL if none has been set and the default algorithm will be used.
  **/
 GtkWidget *
@@ -2296,7 +2296,7 @@ gtk_label_set_attributes (GtkLabel         *label,
  * effective attributes for the label, use
  * pango_layout_get_attribute (gtk_label_get_layout (label)).
  *
- * Returns: (transfer none): the attribute list, or %NULL
+ * Returns: (transfer none) (nullable): the attribute list, or %NULL
  *     if none was set.
  **/
 PangoAttrList *
diff --git a/gtk/gtkmain.c b/gtk/gtkmain.c
index 4513470..5cca733 100644
--- a/gtk/gtkmain.c
+++ b/gtk/gtkmain.c
@@ -312,7 +312,7 @@ gtk_get_interface_age (void)
  * old version of gtk_check_version(), but still get loaded
  * into an application using a newer version of GTK+.
  *
- * Returns: %NULL if the GTK+ library is compatible with the
+ * Returns: (nullable): %NULL if the GTK+ library is compatible with the
  *   given version, or a string describing the version mismatch.
  *   The returned string is owned by GTK+ and should not be modified
  *   or freed.
diff --git a/gtk/gtkmenu.c b/gtk/gtkmenu.c
index 59dfb4a..276e073 100644
--- a/gtk/gtkmenu.c
+++ b/gtk/gtkmenu.c
@@ -2496,7 +2496,7 @@ gtk_menu_set_title (GtkMenu     *menu,
  *
  * Returns the title of the menu. See gtk_menu_set_title().
  *
- * Returns: the title of the menu, or %NULL if the menu
+ * Returns: (nullable): the title of the menu, or %NULL if the menu
  *     has no title set on it. This string is owned by GTK+
  *     and should not be modified or freed.
  *
diff --git a/gtk/gtkmenubutton.c b/gtk/gtkmenubutton.c
index 6d546b5..ae365c7 100644
--- a/gtk/gtkmenubutton.c
+++ b/gtk/gtkmenubutton.c
@@ -823,7 +823,7 @@ gtk_menu_button_set_popup (GtkMenuButton *menu_button,
  * If the button does not use a #GtkMenu, this function
  * returns %NULL.
  *
- * Returns: (transfer none): a #GtkMenu or %NULL
+ * Returns: (transfer none) (nullable): a #GtkMenu or %NULL
  *
  * Since: 3.6
  */
@@ -905,7 +905,7 @@ gtk_menu_button_set_menu_model (GtkMenuButton *menu_button,
  *
  * Returns the #GMenuModel used to generate the popup.
  *
- * Returns: (transfer none): a #GMenuModel or %NULL
+ * Returns: (transfer none) (nullable): a #GMenuModel or %NULL
  *
  * Since: 3.6
  */
@@ -974,7 +974,7 @@ gtk_menu_button_set_align_widget (GtkMenuButton *menu_button,
  *
  * Returns the parent #GtkWidget to use to line up with menu.
  *
- * Returns: (transfer none): a #GtkWidget value or %NULL
+ * Returns: (transfer none) (nullable): a #GtkWidget value or %NULL
  *
  * Since: 3.6
  */
@@ -1220,7 +1220,7 @@ gtk_menu_button_set_popover (GtkMenuButton *menu_button,
  * If the button is not using a #GtkPopover, this function
  * returns %NULL.
  *
- * Returns: (transfer none): a #GtkPopover or %NULL
+ * Returns: (transfer none) (nullable): a #GtkPopover or %NULL
  *
  * Since: 3.12
  */
diff --git a/gtk/gtkmenuitem.c b/gtk/gtkmenuitem.c
index 252b93c..2448935 100644
--- a/gtk/gtkmenuitem.c
+++ b/gtk/gtkmenuitem.c
@@ -1429,7 +1429,7 @@ gtk_menu_item_set_submenu (GtkMenuItem *menu_item,
  * Gets the submenu underneath this menu item, if any.
  * See gtk_menu_item_set_submenu().
  *
- * Returns: (transfer none): submenu for this menu item, or %NULL if none
+ * Returns: (transfer none) (nullable): submenu for this menu item, or %NULL if none
  */
 GtkWidget *
 gtk_menu_item_get_submenu (GtkMenuItem *menu_item)
@@ -2534,7 +2534,7 @@ gtk_menu_item_set_accel_path (GtkMenuItem *menu_item,
  *
  * See gtk_menu_item_set_accel_path() for details.
  *
- * Returns: the accelerator path corresponding to this menu
+ * Returns: (nullable): the accelerator path corresponding to this menu
  *     item’s functionality, or %NULL if not set
  *
  * Since: 2.14
diff --git a/gtk/gtkmodules.c b/gtk/gtkmodules.c
index 8f1aea7..6b50bb1 100644
--- a/gtk/gtkmodules.c
+++ b/gtk/gtkmodules.c
@@ -167,7 +167,7 @@ module_build_la_path (const gchar *directory,
  * Looks for a dynamically module named @name of type @type in the standard GTK+
  *  module search path.
  * 
- * Returns: the pathname to the found module, or %NULL if it wasn’t found.
+ * Returns: (nullable): the pathname to the found module, or %NULL if it wasn’t found.
  *  Free with g_free().
  **/
 gchar *
diff --git a/gtk/gtknativedialog.c b/gtk/gtknativedialog.c
index e4fbb67..d251334 100644
--- a/gtk/gtknativedialog.c
+++ b/gtk/gtknativedialog.c
@@ -496,7 +496,7 @@ gtk_native_dialog_set_title (GtkNativeDialog *self,
  *
  * Gets the title of the #GtkNativeDialog.
  *
- * Returns: the title of the dialog, or %NULL if none has
+ * Returns: (nullable): the title of the dialog, or %NULL if none has
  *    been set explicitly. The returned string is owned by the widget
  *    and must not be modified or freed.
  *
@@ -546,7 +546,7 @@ gtk_native_dialog_set_transient_for (GtkNativeDialog *self,
  * Fetches the transient parent for this window. See
  * gtk_native_dialog_set_transient_for().
  *
- * Returns: (transfer none): the transient parent for this window, or %NULL
+ * Returns: (transfer none) (nullable): the transient parent for this window, or %NULL
  *    if no transient parent has been set.
  *
  * Since: 3.20
diff --git a/gtk/gtknotebook.c b/gtk/gtknotebook.c
index bb50c0b..b5afa58 100644
--- a/gtk/gtknotebook.c
+++ b/gtk/gtknotebook.c
@@ -1128,7 +1128,7 @@ gtk_notebook_class_init (GtkNotebookClass *class)
    * necessary properties to the notebook (e.g. the
    * #GtkNotebook:group-name ).
    *
-   * Returns: (transfer none): a #GtkNotebook that @page should be
+   * Returns: (transfer none) (nullable): a #GtkNotebook that @page should be
    *     added to, or %NULL.
    *
    * Since: 2.12
@@ -7338,7 +7338,7 @@ gtk_notebook_get_current_page (GtkNotebook *notebook)
  *
  * Returns the child widget contained in page number @page_num.
  *
- * Returns: (transfer none): the child widget, or %NULL
+ * Returns: (transfer none) (nullable): the child widget, or %NULL
  *     if @page_num is out of bounds
  */
 GtkWidget*
@@ -7923,7 +7923,7 @@ gtk_notebook_popup_disable (GtkNotebook *notebook)
  * %NULL is returned if @child is not in @notebook or
  * if no tab label has specifically been set for @child.
  *
- * Returns: (transfer none): the tab label
+ * Returns: (transfer none) (nullable): the tab label, or %NULL
  */
 GtkWidget *
 gtk_notebook_get_tab_label (GtkNotebook *notebook,
@@ -8054,7 +8054,7 @@ gtk_notebook_set_tab_label_text (GtkNotebook *notebook,
  * Retrieves the text of the tab label for the page containing
  * @child.
  *
- * Returns: the text of the tab label, or %NULL if the
+ * Returns: (nullable): the text of the tab label, or %NULL if the
  *     tab label widget is not a #GtkLabel. The string is owned
  *     by the widget and must not be freed.
  */
@@ -8082,7 +8082,7 @@ gtk_notebook_get_tab_label_text (GtkNotebook *notebook,
  *
  * Retrieves the menu label widget of the page containing @child.
  *
- * Returns: (transfer none): the menu label, or %NULL if the
+ * Returns: (transfer none) (nullable): the menu label, or %NULL if the
  *     notebook page does not have a menu label other than the
  *     default (the tab label).
  */
@@ -8189,7 +8189,7 @@ gtk_notebook_set_menu_label_text (GtkNotebook *notebook,
  * Retrieves the text of the menu label for the page containing
  * @child.
  *
- * Returns: the text of the tab label, or %NULL if the
+ * Returns: (nullable): the text of the tab label, or %NULL if the
  *     widget does not have a menu label other than the default
  *     menu label, or the menu label widget is not a #GtkLabel.
  *     The string is owned by the widget and must not be freed.
@@ -8415,7 +8415,7 @@ gtk_notebook_set_group_name (GtkNotebook *notebook,
  *
  * Gets the current group name for @notebook.
  *
- * Returns: (transfer none): the group name,
+ * Returns: (transfer none) (nullable): the group name,
  *     or %NULL if none is set.
  *
  * Since: 2.24
@@ -8601,7 +8601,7 @@ gtk_notebook_set_tab_detachable (GtkNotebook *notebook,
  *
  * Gets one of the action widgets. See gtk_notebook_set_action_widget().
  *
- * Returns: (transfer none): The action widget with the given @pack_type
+ * Returns: (transfer none) (nullable): The action widget with the given @pack_type
  *     or %NULL when this action widget has not been set
  *
  * Since: 2.20
diff --git a/gtk/gtkoffscreenwindow.c b/gtk/gtkoffscreenwindow.c
index ec780e5..90185ce 100644
--- a/gtk/gtkoffscreenwindow.c
+++ b/gtk/gtkoffscreenwindow.c
@@ -297,7 +297,7 @@ gtk_offscreen_window_new (void)
  * a #cairo_surface_t.  If you need to keep this around over window
  * resizes then you should add a reference to it.
  *
- * Returns: (transfer none): A #cairo_surface_t pointer to the offscreen
+ * Returns: (transfer none) (nullable): A #cairo_surface_t pointer to the offscreen
  *     surface, or %NULL.
  *
  * Since: 2.20
@@ -319,7 +319,7 @@ gtk_offscreen_window_get_surface (GtkOffscreenWindow *offscreen)
  * and the application should unreference it once it is no longer
  * needed.
  *
- * Returns: (transfer full): A #GdkPixbuf pointer, or %NULL.
+ * Returns: (transfer full) (nullable): A #GdkPixbuf pointer, or %NULL.
  *
  * Since: 2.20
  */
diff --git a/gtk/gtkpagesetup.c b/gtk/gtkpagesetup.c
index aa95703..dabf7a9 100644
--- a/gtk/gtkpagesetup.c
+++ b/gtk/gtkpagesetup.c
@@ -571,7 +571,7 @@ gtk_page_setup_load_file (GtkPageSetup *setup,
  * new #GtkPageSetup object with the restored page setup, 
  * or %NULL if an error occurred. See gtk_page_setup_to_file().
  *
- * Returns: the restored #GtkPageSetup
+ * Returns: (nullable): the restored #GtkPageSetup, or %NULL
  * 
  * Since: 2.12
  */
@@ -711,7 +711,7 @@ out:
  * @key_file. Returns a new #GtkPageSetup object with the restored
  * page setup, or %NULL if an error occurred.
  *
- * Returns: the restored #GtkPageSetup
+ * Returns: (nullable): the restored #GtkPageSetup, or %NULL
  *
  * Since: 2.12
  */
diff --git a/gtk/gtkpaned.c b/gtk/gtkpaned.c
index f7c8da8..9549e97 100644
--- a/gtk/gtkpaned.c
+++ b/gtk/gtkpaned.c
@@ -2216,7 +2216,7 @@ gtk_paned_set_position (GtkPaned *paned,
  * 
  * Obtains the first child of the paned widget.
  * 
- * Returns: (transfer none): first child, or %NULL if it is not set.
+ * Returns: (transfer none) (nullable): first child, or %NULL if it is not set.
  *
  * Since: 2.4
  **/
@@ -2234,7 +2234,7 @@ gtk_paned_get_child1 (GtkPaned *paned)
  * 
  * Obtains the second child of the paned widget.
  * 
- * Returns: (transfer none): second child, or %NULL if it is not set.
+ * Returns: (transfer none) (nullable): second child, or %NULL if it is not set.
  *
  * Since: 2.4
  **/
diff --git a/gtk/gtkpapersize.c b/gtk/gtkpapersize.c
index a9399a6..5545e8c 100644
--- a/gtk/gtkpapersize.c
+++ b/gtk/gtkpapersize.c
@@ -956,7 +956,7 @@ gtk_paper_size_get_default_right_margin (GtkPaperSize *size,
  * Reads a paper size from the group @group_name in the key file
  * @key_file.
  *
- * Returns: a new #GtkPaperSize object with the restored
+ * Returns: (nullable): a new #GtkPaperSize object with the restored
  *     paper size, or %NULL if an error occurred
  *
  * Since: 2.12
diff --git a/gtk/gtkplacessidebar.c b/gtk/gtkplacessidebar.c
index b9517d7..9c9ed90 100644
--- a/gtk/gtkplacessidebar.c
+++ b/gtk/gtkplacessidebar.c
@@ -4608,7 +4608,7 @@ gtk_places_sidebar_set_location (GtkPlacesSidebar *sidebar,
  * function to get the location that is being referred to during the callbacks
  * for your menu items.
  *
- * Returns: (transfer full): a GFile with the selected location, or #NULL if nothing is visually
+ * Returns: (transfer full) (nullable): a GFile with the selected location, or %NULL if nothing is visually
  * selected.
  *
  * Since: 3.10
@@ -5096,8 +5096,8 @@ gtk_places_sidebar_list_shortcuts (GtkPlacesSidebar *sidebar)
  * and returns one of them.  This function is used by #GtkFileChooser to implement
  * the “Alt-1”, “Alt-2”, etc. shortcuts, which activate the cooresponding bookmark.
  *
- * Returns: (transfer full): The bookmark specified by the index @n, or
- * #NULL if no such index exist.  Note that the indices start at 0, even though
+ * Returns: (transfer full) (nullable): The bookmark specified by the index @n, or
+ * %NULL if no such index exist.  Note that the indices start at 0, even though
  * the file chooser starts them with the keyboard shortcut “Alt-1”.
  *
  * Since: 3.10
diff --git a/gtk/gtkplug.c b/gtk/gtkplug.c
index 79ffba3..f9b8180 100644
--- a/gtk/gtkplug.c
+++ b/gtk/gtkplug.c
@@ -379,7 +379,7 @@ gtk_plug_get_embedded (GtkPlug *plug)
  *
  * Retrieves the socket the plug is embedded in.
  *
- * Returns: (transfer none): the window of the socket, or %NULL
+ * Returns: (transfer none) (nullable): the window of the socket, or %NULL
  *
  * Since: 2.14
  **/
diff --git a/gtk/gtkpopover.c b/gtk/gtkpopover.c
index 4c55577..2b82552 100644
--- a/gtk/gtkpopover.c
+++ b/gtk/gtkpopover.c
@@ -2496,7 +2496,7 @@ gtk_popover_set_default_widget (GtkPopover *popover,
  * Gets the widget that should be set as the default while
  * the popover is shown.
  *
- * Returns: (transfer none): the default widget, or %NULL if there is none
+ * Returns: (transfer none) (nullable): the default widget, or %NULL if there is none
  *
  * Since: 3.18
  */
diff --git a/gtk/gtkprintoperation.c b/gtk/gtkprintoperation.c
index 9f4540b..94cf078 100644
--- a/gtk/gtkprintoperation.c
+++ b/gtk/gtkprintoperation.c
@@ -993,7 +993,7 @@ gtk_print_operation_class_init (GtkPrintOperationClass *class)
    * signal is emitted on the operation. Then you can read out any 
    * information you need from the widgets.
    *
-   * Returns: (transfer none): A custom widget that gets embedded in
+   * Returns: (transfer none) (nullable): A custom widget that gets embedded in
    *          the print dialog, or %NULL
    *
    * Since: 2.10
@@ -1576,7 +1576,7 @@ gtk_print_operation_set_print_settings (GtkPrintOperation *op,
  * gtk_print_operation_set_print_settings() or
  * gtk_print_operation_run() have been called.
  *
- * Returns: (transfer none): the current print settings of @op.
+ * Returns: (transfer none) (nullable): the current print settings of @op, or %NULL.
  *
  * Since: 2.10
  **/
diff --git a/gtk/gtkprintsettings.c b/gtk/gtkprintsettings.c
index f2cf860..1191e8e 100644
--- a/gtk/gtkprintsettings.c
+++ b/gtk/gtkprintsettings.c
@@ -1736,7 +1736,7 @@ gtk_print_settings_load_file (GtkPrintSettings *settings,
  * file could not be loaded then error is set to either a #GFileError or
  * #GKeyFileError.  See gtk_print_settings_to_file().
  *
- * Returns: the restored #GtkPrintSettings
+ * Returns: (nullable): the restored #GtkPrintSettings, or %NULL
  * 
  * Since: 2.12
  */
@@ -1829,7 +1829,7 @@ gtk_print_settings_load_key_file (GtkPrintSettings *settings,
  * error occurred. If the file could not be loaded then error is set to either
  * a #GFileError or #GKeyFileError.
  *
- * Returns: the restored #GtkPrintSettings
+ * Returns: (nullable): the restored #GtkPrintSettings, or %NULL
  *
  * Since: 2.12
  */
diff --git a/gtk/gtkprogressbar.c b/gtk/gtkprogressbar.c
index 0a845a0..4ff3bc4 100644
--- a/gtk/gtkprogressbar.c
+++ b/gtk/gtkprogressbar.c
@@ -1440,7 +1440,7 @@ gtk_progress_bar_set_inverted (GtkProgressBar *pbar,
  * to the text, not a copy of it, so will become invalid
  * if you change the text in the progress bar.
  *
- * Returns: text, or %NULL; this string is owned by the widget
+ * Returns: (nullable): text, or %NULL; this string is owned by the widget
  * and should not be modified or freed.
  */
 const gchar*
diff --git a/gtk/gtkrecentfilter.c b/gtk/gtkrecentfilter.c
index bed06a6..bf32dbf 100644
--- a/gtk/gtkrecentfilter.c
+++ b/gtk/gtkrecentfilter.c
@@ -463,7 +463,7 @@ gtk_recent_filter_set_name (GtkRecentFilter *filter,
  * Gets the human-readable name for the filter.
  * See gtk_recent_filter_set_name().
  *
- * Returns: the name of the filter, or %NULL.  The returned string
+ * Returns: (nullable): the name of the filter, or %NULL.  The returned string
  *   is owned by the filter object and should not be freed.
  *
  * Since: 2.10
diff --git a/gtk/gtkrecentmanager.c b/gtk/gtkrecentmanager.c
index b862c17..2b3b996 100644
--- a/gtk/gtkrecentmanager.c
+++ b/gtk/gtkrecentmanager.c
@@ -1162,7 +1162,7 @@ build_recent_info (GBookmarkFile *bookmarks,
  * returns a #GtkRecentInfo-struct containing informations about the resource
  * like its MIME type, or its display name.
  *
- * Returns: a #GtkRecentInfo-struct containing information
+ * Returns: (nullable): a #GtkRecentInfo-struct containing information
  *   about the resource pointed by @uri, or %NULL if the URI was
  *   not registered in the recently used resources list. Free with
  *   gtk_recent_info_unref().
@@ -1969,7 +1969,7 @@ get_icon_fallback (const gchar *icon_name,
  *
  * Retrieves the icon of size @size associated to the resource MIME type.
  *
- * Returns: (transfer full): a #GdkPixbuf containing the icon,
+ * Returns: (transfer full) (nullable): a #GdkPixbuf containing the icon,
  *     or %NULL. Use g_object_unref() when finished using the icon.
  *
  * Since: 2.10
@@ -2004,7 +2004,7 @@ gtk_recent_info_get_icon (GtkRecentInfo *info,
  *
  * Retrieves the icon associated to the resource MIME type.
  *
- * Returns: (transfer full): a #GIcon containing the icon, or %NULL.
+ * Returns: (transfer full) (nullable): a #GIcon containing the icon, or %NULL.
  *   Use g_object_unref() when finished using the icon
  *
  * Since: 2.22
@@ -2267,7 +2267,7 @@ gtk_recent_info_get_short_name (GtkRecentInfo *info)
  * is local, it returns a local path; if the resource is not local,
  * it returns the UTF-8 encoded content of gtk_recent_info_get_uri().
  *
- * Returns: a newly allocated UTF-8 string containing the
+ * Returns: (nullable): a newly allocated UTF-8 string containing the
  *   resource’s URI or %NULL. Use g_free() when done using it.
  *
  * Since: 2.10
@@ -2428,7 +2428,7 @@ gtk_recent_info_has_group (GtkRecentInfo *info,
  *
  * Creates a #GAppInfo for the specified #GtkRecentInfo
  *
- * Returns: (transfer full): the newly created #GAppInfo, or %NULL.
+ * Returns: (transfer full) (nullable): the newly created #GAppInfo, or %NULL.
  *   In case of error, @error will be set either with a
  *   %GTK_RECENT_MANAGER_ERROR or a %G_IO_ERROR
  */
diff --git a/gtk/gtksettings.c b/gtk/gtksettings.c
index 1345584..075aa80 100644
--- a/gtk/gtksettings.c
+++ b/gtk/gtksettings.c
@@ -1903,7 +1903,7 @@ gtk_settings_get_for_screen (GdkScreen *screen)
  * Gets the #GtkSettings object for the default GDK screen, creating
  * it if necessary. See gtk_settings_get_for_screen().
  *
- * Returns: (transfer none): a #GtkSettings object. If there is no default
+ * Returns: (transfer none) (nullall): a #GtkSettings object. If there is no default
  *  screen, then returns %NULL.
  **/
 GtkSettings*
diff --git a/gtk/gtksocket.c b/gtk/gtksocket.c
index 6213ceb..1732d3b 100644
--- a/gtk/gtksocket.c
+++ b/gtk/gtksocket.c
@@ -369,7 +369,7 @@ gtk_socket_get_id (GtkSocket *socket)
  * Retrieves the window of the plug. Use this to check if the plug has
  * been created inside of the socket.
  *
- * Returns: (transfer none): the window of the plug if available, or %NULL
+ * Returns: (transfer none) (nullable): the window of the plug if available, or %NULL
  *
  * Since:  2.14
  **/
diff --git a/gtk/gtkstacksidebar.c b/gtk/gtkstacksidebar.c
index 1212924..3a4efeb 100644
--- a/gtk/gtkstacksidebar.c
+++ b/gtk/gtkstacksidebar.c
@@ -522,7 +522,7 @@ gtk_stack_sidebar_set_stack (GtkStackSidebar *sidebar,
  * Retrieves the stack.
  * See gtk_stack_sidebar_set_stack().
  *
- * Returns: (transfer full): the associated #GtkStack or
+ * Returns: (transfer full) (nullable): the associated #GtkStack or
  *     %NULL if none has been set explicitly
  *
  * Since: 3.16
diff --git a/gtk/gtkstackswitcher.c b/gtk/gtkstackswitcher.c
index e8f3b9b..07719e4 100644
--- a/gtk/gtkstackswitcher.c
+++ b/gtk/gtkstackswitcher.c
@@ -441,7 +441,7 @@ gtk_stack_switcher_set_stack (GtkStackSwitcher *switcher,
  * Retrieves the stack.
  * See gtk_stack_switcher_set_stack().
  *
- * Returns: (transfer none): the stack, or %NULL if
+ * Returns: (transfer none) (nullable): the stack, or %NULL if
  *    none has been set explicitly.
  *
  * Since: 3.10
diff --git a/gtk/gtkstylecontext.c b/gtk/gtkstylecontext.c
index ddf4090..1c2145c 100644
--- a/gtk/gtkstylecontext.c
+++ b/gtk/gtkstylecontext.c
@@ -744,7 +744,7 @@ gtk_style_context_remove_provider_for_screen (GdkScreen        *screen,
  * Shorthand CSS properties cannot be queried for a location and will
  * always return %NULL.
  *
- * Returns: %NULL or the section where value was defined
+ * Returns: (nullable): %NULL or the section where value was defined
  **/
 GtkCssSection *
 gtk_style_context_get_section (GtkStyleContext *context,
@@ -911,7 +911,7 @@ gtk_style_context_set_id (GtkStyleContext *context,
  *
  * Returns the CSS ID used when rendering.
  *
- * Returns: the ID or %NULL if no ID is set.
+ * Returns: (nullable): the ID or %NULL if no ID is set.
  **/
 const char *
 gtk_style_context_get_id (GtkStyleContext *context)
@@ -1168,7 +1168,7 @@ gtk_style_context_set_parent (GtkStyleContext *context,
  * Gets the parent context set via gtk_style_context_set_parent().
  * See that function for details.
  *
- * Returns: (transfer none): the parent context or %NULL
+ * Returns: (transfer none) (nullable): the parent context or %NULL
  *
  * Since: 3.4
  **/
@@ -1897,7 +1897,7 @@ gtk_style_context_get_style (GtkStyleContext *context,
  * the default icon factory, returning an icon set if found, otherwise
  * %NULL.
  *
- * Returns: (transfer none): The looked  up %GtkIconSet, or %NULL
+ * Returns: (transfer none) (nullable): The looked  up %GtkIconSet, or %NULL
  *
  * Deprecated: 3.10: Use gtk_icon_theme_lookup_icon() instead.
  **/
@@ -2014,7 +2014,7 @@ gtk_style_context_set_frame_clock (GtkStyleContext *context,
  *
  * Returns the #GdkFrameClock to which @context is attached.
  *
- * Returns: (transfer none): a #GdkFrameClock, or %NULL
+ * Returns: (transfer none) (nullable): a #GdkFrameClock, or %NULL
  *  if @context does not have an attached frame clock.
  *
  * Since: 3.8
@@ -3024,7 +3024,7 @@ gtk_draw_insertion_cursor (GtkWidget          *widget,
  *
  * FIXME 4.0: Make this part of the signal.
  *
- * Returns: %NULL or the currently invalidating changes
+ * Returns: (nullable): %NULL or the currently invalidating changes
  **/
 const GtkBitmask *
 _gtk_style_context_get_changes (GtkStyleContext *context)
diff --git a/gtk/gtkstyleproperty.c b/gtk/gtkstyleproperty.c
index 9639ae4..4ce68b2 100644
--- a/gtk/gtkstyleproperty.c
+++ b/gtk/gtkstyleproperty.c
@@ -142,7 +142,7 @@ _gtk_style_property_init (GtkStyleProperty *property)
  * always be a #GtkCssValue whose values can be queried with
  * _gtk_css_array_value_get_nth().
  *
- * Returns: %NULL on failure or the parsed #GtkCssValue
+ * Returns: (nullable): %NULL on failure or the parsed #GtkCssValue
  **/
 GtkCssValue *
 _gtk_style_property_parse_value (GtkStyleProperty *property,
@@ -260,7 +260,7 @@ _gtk_style_property_add_alias (const gchar *name,
  * Looks up the CSS property with the given @name. If no such
  * property exists, %NULL is returned.
  *
- * Returns: (transfer none): The property or %NULL if no
+ * Returns: (transfer none) (nullable): The property or %NULL if no
  *     property with the given name exists.
  **/
 GtkStyleProperty *
diff --git a/gtk/gtkstyleprovider.c b/gtk/gtkstyleprovider.c
index fab975a..6b2f560 100644
--- a/gtk/gtkstyleprovider.c
+++ b/gtk/gtkstyleprovider.c
@@ -62,7 +62,7 @@ gtk_style_provider_iface_init (gpointer g_iface)
  * Returns the style settings affecting a widget defined by @path, or %NULL if
  * @provider doesn’t contemplate styling @path.
  *
- * Returns: (transfer full): a #GtkStyleProperties containing the
+ * Returns: (transfer full) (nullable): a #GtkStyleProperties containing the
  * style settings affecting @path
  *
  * Since: 3.0
@@ -132,7 +132,7 @@ gtk_style_provider_get_style_property (GtkStyleProvider *provider,
  * Returns the #GtkIconFactory defined to be in use for @path, or %NULL if none
  * is defined.
  *
- * Returns: (transfer none): The icon factory to use for @path, or %NULL
+ * Returns: (transfer none) (nullable): The icon factory to use for @path, or %NULL
  *
  * Since: 3.0
  *
diff --git a/gtk/gtktestutils.c b/gtk/gtktestutils.c
index 72da6c5..e911e65 100644
--- a/gtk/gtktestutils.c
+++ b/gtk/gtktestutils.c
@@ -439,7 +439,7 @@ gtk_test_find_sibling (GtkWidget *base_widget,
  * gtk_test_widget_click() for possible caveats involving the search of
  * such widgets and synthesizing widget events.
  *
- * Returns: (transfer none): a valid widget if any is found or %NULL.
+ * Returns: (transfer none) (nullable): a valid widget if any is found or %NULL.
  *
  * Since: 2.14
  **/
diff --git a/gtk/gtktextbuffer.c b/gtk/gtktextbuffer.c
index 41ef4a3..1597b4b 100644
--- a/gtk/gtktextbuffer.c
+++ b/gtk/gtktextbuffer.c
@@ -2251,7 +2251,7 @@ gtk_text_buffer_delete_mark (GtkTextBuffer *buffer,
  * Returns the mark named @name in buffer @buffer, or %NULL if no such
  * mark exists in the buffer.
  *
- * Returns: (transfer none): a #GtkTextMark, or %NULL
+ * Returns: (transfer none) (nullable): a #GtkTextMark, or %NULL
  **/
 GtkTextMark*
 gtk_text_buffer_get_mark (GtkTextBuffer *buffer,
diff --git a/gtk/gtktextbufferrichtext.h b/gtk/gtktextbufferrichtext.h
index 75cf2d6..ccb040b 100644
--- a/gtk/gtktextbufferrichtext.h
+++ b/gtk/gtktextbufferrichtext.h
@@ -40,7 +40,7 @@ G_BEGIN_DECLS
  * A function that is called to serialize the content of a text buffer.
  * It must return the serialized form of the content.
  *
- * Returns: a newly-allocated array of guint8 which contains the serialized
+ * Returns: (nullable): a newly-allocated array of guint8 which contains the serialized
  *   data, or %NULL if an error occurred
  */
 typedef guint8 * (* GtkTextBufferSerializeFunc)   (GtkTextBuffer     *register_buffer,
diff --git a/gtk/gtktextmark.c b/gtk/gtktextmark.c
index dc8f78c..b645094 100644
--- a/gtk/gtktextmark.c
+++ b/gtk/gtktextmark.c
@@ -294,7 +294,7 @@ gtk_text_mark_get_visible (GtkTextMark *mark)
  * 
  * Returns the mark name; returns NULL for anonymous marks.
  * 
- * Returns: mark name
+ * Returns: (nullable): mark name, or %NULL
  **/
 const char *
 gtk_text_mark_get_name (GtkTextMark *mark)
diff --git a/gtk/gtktexttagtable.c b/gtk/gtktexttagtable.c
index 42569cf..c44c0d9 100644
--- a/gtk/gtktexttagtable.c
+++ b/gtk/gtktexttagtable.c
@@ -289,7 +289,7 @@ gtk_text_tag_table_add (GtkTextTagTable *table,
  * 
  * Look up a named tag.
  * 
- * Returns: (transfer none): The tag, or %NULL if none by that name is in the table.
+ * Returns: (transfer none) (nullable): The tag, or %NULL if none by that name is in the table.
  **/
 GtkTextTag*
 gtk_text_tag_table_lookup (GtkTextTagTable *table,
diff --git a/gtk/gtktextview.c b/gtk/gtktextview.c
index d6c4aa1..8539d9d 100644
--- a/gtk/gtktextview.c
+++ b/gtk/gtktextview.c
@@ -3460,7 +3460,7 @@ gtk_text_view_set_tabs (GtkTextView   *text_view,
  * “standard” (8-space) tabs are used. Free the return value
  * with pango_tab_array_free().
  * 
- * Returns: copy of default tab array, or %NULL if “standard” 
+ * Returns: (nullable): copy of default tab array, or %NULL if “standard” 
  *    tabs are used; must be freed with pango_tab_array_free().
  **/
 PangoTabArray*
@@ -10210,7 +10210,7 @@ text_window_get_height (GtkTextWindow *win)
  * height is 0, and are nonexistent before the widget has been
  * realized.
  *
- * Returns: (transfer none): a #GdkWindow, or %NULL
+ * Returns: (transfer none) (nullable): a #GdkWindow, or %NULL
  **/
 GdkWindow*
 gtk_text_view_get_window (GtkTextView *text_view,
diff --git a/gtk/gtktoolbar.c b/gtk/gtktoolbar.c
index 7900857..97d205e 100644
--- a/gtk/gtktoolbar.c
+++ b/gtk/gtktoolbar.c
@@ -2893,7 +2893,7 @@ gtk_toolbar_get_n_items (GtkToolbar *toolbar)
  * Returns the @n'th item on @toolbar, or %NULL if the
  * toolbar does not contain an @n'th item.
  *
- * Returns: (transfer none): The @n'th #GtkToolItem on @toolbar,
+ * Returns: (transfer none) (nullable): The @n'th #GtkToolItem on @toolbar,
  *     or %NULL if there isn’t an @n'th item.
  *
  * Since: 2.4
diff --git a/gtk/gtktoolbutton.c b/gtk/gtktoolbutton.c
index eadb362..b46399c 100644
--- a/gtk/gtktoolbutton.c
+++ b/gtk/gtktoolbutton.c
@@ -1217,7 +1217,7 @@ gtk_tool_button_set_label (GtkToolButton *button,
  * doesn’t have a label. or uses a the label from a stock item. The returned
  * string is owned by GTK+, and must not be modified or freed.
  * 
- * Returns: The label, or %NULL
+ * Returns: (nullable): The label, or %NULL
  * 
  * Since: 2.4
  **/
@@ -1372,7 +1372,7 @@ gtk_tool_button_set_icon_name (GtkToolButton *button,
  * Returns the name of the themed icon for the tool button,
  * see gtk_tool_button_set_icon_name().
  *
- * Returns: the icon name or %NULL if the tool button has
+ * Returns: (nullable): the icon name or %NULL if the tool button has
  * no themed icon
  *
  * Since: 2.8
@@ -1478,7 +1478,7 @@ gtk_tool_button_set_label_widget (GtkToolButton *button,
  * Returns the widget used as label on @button.
  * See gtk_tool_button_set_label_widget().
  *
- * Returns: (transfer none): The widget used as label
+ * Returns: (transfer none) (nullable): The widget used as label
  *     on @button, or %NULL.
  *
  * Since: 2.4
@@ -1498,7 +1498,7 @@ gtk_tool_button_get_label_widget (GtkToolButton *button)
  * Return the widget used as icon widget on @button.
  * See gtk_tool_button_set_icon_widget().
  *
- * Returns: (transfer none): The widget used as icon
+ * Returns: (transfer none) (nullable): The widget used as icon
  *     on @button, or %NULL.
  *
  * Since: 2.4
diff --git a/gtk/gtktoolitemgroup.c b/gtk/gtktoolitemgroup.c
index c4dbbcb..b8c5fbe 100644
--- a/gtk/gtktoolitemgroup.c
+++ b/gtk/gtktoolitemgroup.c
@@ -2010,7 +2010,7 @@ gtk_tool_item_group_set_ellipsize (GtkToolItemGroup   *group,
  *
  * Gets the label of @group.
  *
- * Returns: the label of @group. The label is an internal string of @group
+ * Returns: (nullable): the label of @group. The label is an internal string of @group
  *     and must not be modified. Note that %NULL is returned if a custom
  *     label has been set with gtk_tool_item_group_set_label_widget()
  *
diff --git a/gtk/gtktoolpalette.c b/gtk/gtktoolpalette.c
index c51fb0b..7f556c1 100644
--- a/gtk/gtktoolpalette.c
+++ b/gtk/gtktoolpalette.c
@@ -1489,7 +1489,7 @@ gtk_tool_palette_get_expand (GtkToolPalette   *palette,
  * Gets the item at position (x, y).
  * See gtk_tool_palette_get_drop_group().
  *
- * Returns: (transfer none): the #GtkToolItem at position or %NULL if there is no such item
+ * Returns: (transfer none) (nullable): the #GtkToolItem at position or %NULL if there is no such item
  *
  * Since: 2.20
  */
@@ -1521,7 +1521,7 @@ gtk_tool_palette_get_drop_item (GtkToolPalette *palette,
  *
  * Gets the group at position (x, y).
  *
- * Returns: (transfer none): the #GtkToolItemGroup at position or %NULL
+ * Returns: (transfer none) (nullable): the #GtkToolItemGroup at position or %NULL
  *     if there is no such group
  *
  * Since: 2.20
diff --git a/gtk/gtktreemodel.c b/gtk/gtktreemodel.c
index d919f58..fd7527e 100644
--- a/gtk/gtktreemodel.c
+++ b/gtk/gtktreemodel.c
@@ -611,7 +611,7 @@ gtk_tree_path_new (void)
  * child of that 11th child, and the 1st child of that 5th child.
  * If an invalid path string is passed in, %NULL is returned.
  *
- * Returns: A newly-created #GtkTreePath-struct, or %NULL
+ * Returns: (nullable): A newly-created #GtkTreePath-struct, or %NULL
  */
 GtkTreePath *
 gtk_tree_path_new_from_string (const gchar *path)
@@ -862,7 +862,7 @@ gtk_tree_path_get_depth (GtkTreePath *path)
  *
  * The length of the array can be obtained with gtk_tree_path_get_depth().
  *
- * Returns: The current indices, or %NULL
+ * Returns: (nullable): The current indices, or %NULL
  */
 gint *
 gtk_tree_path_get_indices (GtkTreePath *path)
@@ -2334,7 +2334,7 @@ gtk_tree_row_reference_new (GtkTreeModel *model,
  * need to carefully monitor exactly when a row reference updates
  * itself, and is not generally needed by most applications.
  *
- * Returns: a newly allocated #GtkTreeRowReference, or %NULL
+ * Returns: (nullable): a newly allocated #GtkTreeRowReference, or %NULL
  */
 GtkTreeRowReference *
 gtk_tree_row_reference_new_proxy (GObject      *proxy,
diff --git a/gtk/gtktreemodelfilter.c b/gtk/gtktreemodelfilter.c
index 7b77ef1..e651c81 100644
--- a/gtk/gtktreemodelfilter.c
+++ b/gtk/gtktreemodelfilter.c
@@ -4128,7 +4128,7 @@ gtk_real_tree_model_filter_convert_child_path_to_path (GtkTreeModelFilter *filte
  * child model or points to a row which is not visible in @filter, then %NULL
  * is returned.
  *
- * Returns: A newly allocated #GtkTreePath, or %NULL.
+ * Returns: (nullable): A newly allocated #GtkTreePath, or %NULL.
  *
  * Since: 2.4
  */
@@ -4171,7 +4171,7 @@ gtk_tree_model_filter_convert_child_path_to_path (GtkTreeModelFilter *filter,
  * point to the same location in the model not being filtered. If @filter_path
  * does not point to a location in the child model, %NULL is returned.
  *
- * Returns: A newly allocated #GtkTreePath, or %NULL.
+ * Returns: (nullable): A newly allocated #GtkTreePath, or %NULL.
  *
  * Since: 2.4
  */
diff --git a/gtk/gtktreemodelsort.c b/gtk/gtktreemodelsort.c
index 6cef856..a8a44df 100644
--- a/gtk/gtktreemodelsort.c
+++ b/gtk/gtktreemodelsort.c
@@ -2289,7 +2289,7 @@ gtk_real_tree_model_sort_convert_child_path_to_path (GtkTreeModelSort *tree_mode
  * point to the same row in the sorted model.  If @child_path isn’t a valid 
  * path on the child model, then %NULL is returned.
  * 
- * Returns: A newly allocated #GtkTreePath, or %NULL
+ * Returns: (nullable): A newly allocated #GtkTreePath, or %NULL
  **/
 GtkTreePath *
 gtk_tree_model_sort_convert_child_path_to_path (GtkTreeModelSort *tree_model_sort,
@@ -2362,7 +2362,7 @@ gtk_tree_model_sort_convert_child_iter_to_iter (GtkTreeModelSort *tree_model_sor
  * sorted.  If @sorted_path does not point to a location in the child model, 
  * %NULL is returned.
  * 
- * Returns: A newly allocated #GtkTreePath, or %NULL
+ * Returns: (nullable): A newly allocated #GtkTreePath, or %NULL
  **/
 GtkTreePath *
 gtk_tree_model_sort_convert_path_to_child_path (GtkTreeModelSort *tree_model_sort,
diff --git a/gtk/gtktreeview.c b/gtk/gtktreeview.c
index a4bd8aa..58a30c0 100644
--- a/gtk/gtktreeview.c
+++ b/gtk/gtktreeview.c
@@ -11516,7 +11516,7 @@ gtk_tree_view_get_selection (GtkTreeView *tree_view)
  *
  * Gets the #GtkAdjustment currently being used for the horizontal aspect.
  *
- * Returns: (transfer none): A #GtkAdjustment object, or %NULL
+ * Returns: (transfer none) (nullable): A #GtkAdjustment object, or %NULL
  *     if none is currently being used.
  *
  * Deprecated: 3.0: Use gtk_scrollable_get_hadjustment()
@@ -11592,7 +11592,7 @@ gtk_tree_view_do_set_hadjustment (GtkTreeView   *tree_view,
  *
  * Gets the #GtkAdjustment currently being used for the vertical aspect.
  *
- * Returns: (transfer none): A #GtkAdjustment object, or %NULL
+ * Returns: (transfer none) (nullable): A #GtkAdjustment object, or %NULL
  *     if none is currently being used.
  *
  * Deprecated: 3.0: Use gtk_scrollable_get_vadjustment()
@@ -12240,7 +12240,7 @@ gtk_tree_view_get_n_columns (GtkTreeView *tree_view)
  *
  * Gets the #GtkTreeViewColumn at the given position in the #tree_view.
  *
- * Returns: (transfer none): The #GtkTreeViewColumn, or %NULL if the
+ * Returns: (transfer none) (nullable): The #GtkTreeViewColumn, or %NULL if the
  *     position is outside the range of columns.
  **/
 GtkTreeViewColumn *
@@ -13427,7 +13427,7 @@ gtk_tree_view_set_cursor_on_cell (GtkTreeView       *tree_view,
  * This is used primarily to compare to `event->window`
  * to confirm that the event on @tree_view is on the right window.
  *
- * Returns: (transfer none): A #GdkWindow, or %NULL when @tree_view
+ * Returns: (transfer none) (nullable): A #GdkWindow, or %NULL when @tree_view
  *     hasn’t been realized yet
  **/
 GdkWindow *
@@ -14884,7 +14884,7 @@ gtk_tree_view_set_search_equal_func (GtkTreeView                *tree_view,
  * entry for @tree_view.  In case the built-in entry is being used, %NULL
  * will be returned.
  *
- * Returns: (transfer none): the entry currently in use as search entry.
+ * Returns: (transfer none) (nullable): the entry currently in use as search entry.
  *
  * Since: 2.10
  */
diff --git a/gtk/gtktreeviewcolumn.c b/gtk/gtktreeviewcolumn.c
index d5e9ae1..b78062e 100644
--- a/gtk/gtktreeviewcolumn.c
+++ b/gtk/gtktreeviewcolumn.c
@@ -2520,7 +2520,7 @@ gtk_tree_view_column_set_widget (GtkTreeViewColumn *tree_column,
  * Returns the #GtkWidget in the button on the column header.
  * If a custom widget has not been set then %NULL is returned.
  *
- * Returns: (transfer none): The #GtkWidget in the column
+ * Returns: (transfer none) (nullable): The #GtkWidget in the column
  *     header, or %NULL
  **/
 GtkWidget *
@@ -3101,7 +3101,7 @@ gtk_tree_view_column_queue_resize (GtkTreeViewColumn *tree_column)
  * If @column is currently not inserted in any tree view, %NULL is
  * returned.
  *
- * Returns: (transfer none): The tree view wherein @column has
+ * Returns: (transfer none) (nullable): The tree view wherein @column has
  *     been inserted if any, %NULL otherwise.
  *
  * Since: 2.12
diff --git a/gtk/gtkwidget.c b/gtk/gtkwidget.c
index 7656bcd..8f5f478 100644
--- a/gtk/gtkwidget.c
+++ b/gtk/gtkwidget.c
@@ -5749,7 +5749,7 @@ gtk_widget_queue_resize_no_redraw (GtkWidget *widget)
  *
  * Unrealized widgets do not have a frame clock.
  *
- * Returns: (transfer none): a #GdkFrameClock (or #NULL if widget is unrealized)
+ * Returns: (transfer none) (nullable): a #GdkFrameClock (or #NULL if widget is unrealized)
  *
  * Since: 3.8
  */
@@ -11891,7 +11891,7 @@ gtk_widget_set_composite_name (GtkWidget   *widget,
  *
  * Obtains the composite name of a widget.
  *
- * Returns: the composite name of @widget, or %NULL if @widget is not
+ * Returns: (nullable): the composite name of @widget, or %NULL if @widget is not
  *   a composite child. The string should be freed when it is no
  *   longer needed.
  *
@@ -13173,7 +13173,7 @@ gtk_widget_class_install_style_property (GtkWidgetClass *klass,
  *
  * Finds a style property of a widget class by name.
  *
- * Returns: (transfer none): the #GParamSpec of the style property or
+ * Returns: (transfer none) (nullable): the #GParamSpec of the style property or
  *   %NULL if @class has no style property with that name.
  *
  * Since: 2.2
diff --git a/gtk/gtkwidgetpath.c b/gtk/gtkwidgetpath.c
index f28ddc9..9ca546d 100644
--- a/gtk/gtkwidgetpath.c
+++ b/gtk/gtkwidgetpath.c
@@ -465,7 +465,7 @@ gtk_widget_path_append_with_siblings (GtkWidgetPath *path,
  * Returns the list of siblings for the element at @pos. If the element
  * was not added with siblings, %NULL is returned.
  *
- * Returns: %NULL or the list of siblings for the element at @pos.
+ * Returns: (nullable): %NULL or the list of siblings for the element at @pos.
  **/
 const GtkWidgetPath *
 gtk_widget_path_iter_get_siblings (const GtkWidgetPath *path,
@@ -519,7 +519,7 @@ gtk_widget_path_iter_get_sibling_index (const GtkWidgetPath *path,
  * Returns the object name that is at position @pos in the widget
  * hierarchy defined in @path.
  *
- * Returns: the name or %NULL
+ * Returns: (nullable): the name or %NULL
  *
  * Since: 3.20
  **/
@@ -709,7 +709,7 @@ gtk_widget_path_iter_set_state (GtkWidgetPath *path,
  * the position @pos in the widget hierarchy defined by
  * @path
  *
- * Returns: The widget name, or %NULL if none was set.
+ * Returns: (nullable): The widget name, or %NULL if none was set.
  **/
 const gchar *
 gtk_widget_path_iter_get_name (const GtkWidgetPath *path,
diff --git a/gtk/gtkwindow.c b/gtk/gtkwindow.c
index 97c6e1f..8d94196 100644
--- a/gtk/gtkwindow.c
+++ b/gtk/gtkwindow.c
@@ -10824,7 +10824,7 @@ gtk_window_has_toplevel_focus (GtkWindow *window)
  * @window is %NULL or if @window does not have an explicit
  * window group.
  *
- * Returns: (transfer none): the #GtkWindowGroup for a window or the default group
+ * Returns: (transfer none) (nullable): the #GtkWindowGroup for a window or the default group
  *
  * Since: 2.10
  */
@@ -12089,7 +12089,7 @@ _gtk_window_get_popover_position (GtkWindow             *window,
  * Returns the conceptual parent of this popover, the real
  * parent will always be @window.
  *
- * Returns: The conceptual parent widget, or %NULL.
+ * Returns: (nullable): The conceptual parent widget, or %NULL.
  **/
 GtkWidget *
 _gtk_window_get_popover_parent (GtkWindow *window,
diff --git a/gtk/gtkwindowgroup.c b/gtk/gtkwindowgroup.c
index bed78cf..a3a6985 100644
--- a/gtk/gtkwindowgroup.c
+++ b/gtk/gtkwindowgroup.c
@@ -337,7 +337,7 @@ _gtk_window_group_remove_device_grab (GtkWindowGroup *window_group,
  *
  * Returns the current grab widget for @device, or %NULL if none.
  *
- * Returns: (transfer none): The grab widget, or %NULL
+ * Returns: (transfer none) (nullable): The grab widget, or %NULL
  *
  * Since: 3.0
  */
