The following vala code:

<vala code>
            this.search.Query (0,
                               this.category,
                               new string[0],
                               "",   
                               new string[0],
                               "",
                               false,
                               new string[0],
                               false,
                               0,
                               -1,
                               on_search_query_cb);
...

    private void on_search_query_cb (string[][] search_result,
                                     GLib.Error error) {
</vala code>

generates following C code:

<c code>
static void rygel_tracker_category_on_search_query_cb (RygelTrackerCategory* self, char*** search_result, int search_result_length1, GError* error) {
...

static void _rygel_tracker_category_on_search_query_cb_cb (DBusGProxy* proxy, DBusGProxyCall* call, void* user_data) {
    GError* error;
    GPtrArray* search_result;
    error = NULL;
    dbus_g_proxy_end_call (proxy, call, &error, dbus_g_type_get_collection ("GPtrArray", G_TYPE_STRV), &search_result, G_TYPE_INVALID);
    rygel_tracker_category_on_search_query_cb (user_data, search_result->pdata, search_result->len, error);
}

...
    dbus_g_proxy_begin_call (self, "Query", _rygel_tracker_category_on_search_query_cb_cb, param12_target, NULL, G_TYPE_INT, param1, G_TYPE_STRING, param2, G_TYPE_STRV, param3, G_TYPE_STRING, param4, G_TYPE_STRV, param5, G_TYPE_STRING, param6, G_TYPE_BOOLEAN, param7, G_TYPE_STRV, param8, G_TYPE_BOOLEAN, param9, G_TYPE_INT, param10, G_TYPE_INT, param11, G_TYPE_INVALID, G_TYPE_INVALID);
</c code>

The problem is search_result->pdata above is not being casted to "char ***" before getting passed to rygel_tracker_category_on_search_query_cb as it should be and therefore C compiler warns about it.