Pinta doesn't quit and instead throws unhandled exception

[T Chen]

Platform: Ubuntu 13.10 32-bit running Cinnamon 2.0.14 as desktop environment
Steps to reproduce:
1) Open a picture
2) Make edits to the picture
3) Save edited picture
4) Quit Pinta by clicking the Close button on the titlebar
5) The following error will appear:

Unhandled exception:
Exception has been thrown by the target of an invocation.

System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.NullReferenceException: Object reference not set to an instance of an object
  at Pinta.Core.SettingsManager.Serialize (System.String filename, System.Collections.Generic.Dictionary`2 settings) [0x00000] in <filename unknown>:0
  at Pinta.Core.SettingsManager.SaveSettings () [0x00000] in <filename unknown>:0
  at Pinta.MainWindow.SaveUserSettings () [0x00000] in <filename unknown>:0
  at Pinta.MainWindow.<MainWindow>m__34 (System.Object , System.EventArgs ) [0x00000] in <filename unknown>:0
  at Pinta.Core.FileActions.RaiseBeforeQuit () [0x00000] in <filename unknown>:0
  at Pinta.Actions.ExitProgramAction.Activated (System.Object sender, System.EventArgs e) [0x00000] in <filename unknown>:0
  at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (System.Reflection.MonoMethod,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] in <filename unknown>:0
  --- 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] in <filename unknown>:0
  at System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) [0x00000] in <filename unknown>:0
  at System.Delegate.DynamicInvokeImpl (System.Object[] args) [0x00000] in <filename unknown>:0
  at System.MulticastDelegate.DynamicInvokeImpl (System.Object[] args) [0x00000] in <filename unknown>:0
  at System.Delegate.DynamicInvoke (System.Object[] args) [0x00000] in <filename unknown>:0
  at GLib.Signal.ClosureInvokedCB (System.Object o, GLib.ClosureInvokedArgs args) [0x00000] in <filename unknown>:0
  at GLib.SignalClosure.Invoke (GLib.ClosureInvokedArgs args) [0x00000] in <filename unknown>:0
  at GLib.SignalClosure.MarshalCallback (IntPtr raw_closure, IntPtr return_val, UInt32 n_param_vals, IntPtr param_values, IntPtr invocation_hint, IntPtr marshal_data) [0x00000] in <filename unknown>:0

Running Pinta from a terminal gives the following output (note: $ is just the shell prompt):

$ pinta

(Pinta:7240): GLib-GObject-WARNING **: Attempt to add property __gtksharp_11_Pinta_Gui_Widgets_CellRendererSurface::surface after class was initialised
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
$

The first line appears to not be a problem; however, the last line only appears when this bug occurs.

Also, when running Pinta, when I look at System Monitor I can't find any program named "pinta". Does Pinta run under another name, or is there something wrong?

[Cameron White (cameronwhite91)]

Fixed: https://github.com/PintaProject/Pinta/commit/eac16ee0ded0c410c991383f49392177275bee88