Marshaling activate signal
Exception in Gtk# callback delegate
  Note: Applications can use GLib.ExceptionManager.UnhandledException to handle the exception.
System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.ArgumentNullException: Argument cannot be null.
Parameter name: path2
  at System.IO.Path.Combine (System.String path1, System.String path2) [0x00000] 
  at Hyena.XdgBaseDirectorySpec.GetXdgDirectoryUnderHome (System.String key, System.String fallback) [0x00000] 
  at PdfMod.Gui.Client.<CreateChooser>m__A (System.String s) [0x00000] 
  at System.Linq.Enumerable+<CreateSelectIterator>c__Iterator10`2[System.String,System.String].MoveNext () [0x00000] 
  at System.Linq.Enumerable+<CreateWhereIterator>c__Iterator1D`1[System.String].MoveNext () [0x00000] 
  at System.Collections.Generic.List`1[System.String].AddEnumerable (IEnumerable`1 enumerable) [0x00000] 
  at System.Collections.Generic.List`1[System.String]..ctor (IEnumerable`1 collection) [0x00000] 
  at System.Linq.Enumerable.ToArray[String] (IEnumerable`1 source) [0x00000] 
  at PdfMod.Gui.Client.CreateChooser (System.String title, FileChooserAction action) [0x00000] 
  at PdfMod.Gui.Actions.OnOpen (System.Object o, System.EventArgs args) [0x00000] 
  at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (object,object[],System.Exception&)
  at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] 
  --- End of inner exception stack trace ---
  at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] 
  at System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) [0x00000] 
  at System.Delegate.DynamicInvokeImpl (System.Object[] args) [0x00000] 
  at System.MulticastDelegate.DynamicInvokeImpl (System.Object[] args) [0x00000] 
  at System.Delegate.DynamicInvoke (System.Object[] args) [0x00000] 
  at GLib.Signal.ClosureInvokedCB (System.Object o, GLib.ClosureInvokedArgs args) [0x00000] 
  at GLib.SignalClosure.Invoke (GLib.ClosureInvokedArgs args) [0x00000] 
  at GLib.SignalClosure.MarshalCallback (IntPtr raw_closure, IntPtr return_val, UInt32 n_param_vals, IntPtr param_values, IntPtr invocation_hint, IntPtr marshal_data) [0x00000] 
   at GLib.ExceptionManager.RaiseUnhandledException(System.Exception e, Boolean is_terminal)
   at GLib.SignalClosure.MarshalCallback(IntPtr raw_closure, IntPtr return_val, UInt32 n_param_vals, IntPtr param_values, IntPtr invocation_hint, IntPtr marshal_data)
   at Gtk.Application.gtk_main()
   at Gtk.Application.Run()
   at PdfMod.Gui.Client..ctor(Boolean loadFiles)
   at PdfMod.PdfMod.Main(System.String[] args)
