Animation Window gives 400 errors NullReferenceException

2) How can we reproduce it using the example you attached
1 Create new project
2 Add to any window (e.g. Project view) Animation Window-tab and make it notvisible by opening another tab
3 Press play
4 Make Animation Window-tab visible

Actual result: the Editor hangs for few seconds and gives few hundreds of errors:

NullReferenceException: Object reference not set to an instance of an object
UnityEditor.AnimationWindow.OnGUI () (at C:/buildslave/unity/build/Editor/Mono/Animation/AnimationWindow/Deprecated/AnimationWindow.cs:1307)
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-runtime-and-classlibs/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:222)