Reproduction Steps:
1. In the Menu, select "Test/Test".
2. Mouse over to the opened window.
3. Observe console.

Expected results: The stack trace for the exception should be thrown.
Actual results: The stack trace is wrapped by the editor.

Reproducible in: 2017.1.0a6, 2017.1.0b2

Here's the stacktrace in .NET 4.6:

NullReferenceException: Object reference not set to an instance of an object
UnityEditor.HostView.InvokeOnGUI (UnityEngine.Rect onGUIPosition) (at C:/buildslave/unity/build/Editor/Mono/HostView.cs:238)
UnityEditor.DockArea.OldOnGUI () (at C:/buildslave/unity/build/Editor/Mono/GUI/DockArea.cs:407)
UnityEngine.Experimental.UIElements.IMGUIContainer.DoOnGUI (UnityEngine.Event evt) (at C:/buildslave/unity/build/Runtime/UIElements/Managed/IMGUIContainer.cs:103)
UnityEngine.Experimental.UIElements.IMGUIContainer.HandleEvent (UnityEngine.Event evt, UnityEngine.Experimental.UIElements.VisualElement finalTarget) (at C:/buildslave/unity/build/Runtime/UIElements/Managed/IMGUIContainer.cs:137)
UnityEngine.Experimental.UIElements.IMGUIContainer.DoRepaint (UnityEngine.IStylePainter painter) (at C:/buildslave/unity/build/Runtime/UIElements/Managed/IMGUIContainer.cs:36)
UnityEngine.Experimental.UIElements.Panel.PaintSubTree (UnityEngine.Event e, UnityEngine.Experimental.UIElements.VisualElement root, UnityEngine.Matrix4x4 offset, UnityEngine.Rect currentClip, UnityEngine.Matrix4x4 clipTransform, UnityEngine.Rect currentGlobalClip) (at C:/buildslave/unity/build/Runtime/UIElements/Managed/Panel.cs:390)
UnityEngine.Experimental.UIElements.Panel.PaintSubTree (UnityEngine.Event e, UnityEngine.Experimental.UIElements.VisualElement root, UnityEngine.Matrix4x4 offset, UnityEngine.Rect currentClip, UnityEngine.Matrix4x4 clipTransform, UnityEngine.Rect currentGlobalClip) (at C:/buildslave/unity/build/Runtime/UIElements/Managed/Panel.cs:398)
UnityEngine.Experimental.UIElements.Panel.Repaint (UnityEngine.Event e) (at C:/buildslave/unity/build/Runtime/UIElements/Managed/Panel.cs:411)
UnityEngine.Experimental.UIElements.UIElementsUtility.DoDispatch (UnityEngine.Experimental.UIElements.IVisualElementPanel panel) (at C:/buildslave/unity/build/Runtime/UIElements/Managed/UIElementsUtility.cs:203)
UnityEngine.Experimental.UIElements.UIElementsUtility.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr) (at C:/buildslave/unity/build/Runtime/UIElements/Managed/UIElementsUtility.cs:67)
UnityEngine.GUIUtility.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr) (at C:/buildslave/unity/build/Runtime/IMGUI/Managed/GUIUtility.cs:186)

Here's the stacktrace in .NET 3.5:

NullReferenceException: Object reference not set to an instance of an object
TestEditor.OnGUI () (at Assets/Editor/TestEditor.cs:22)
System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:222)