To reproduce:
1. open the attached project and the animator
2. observe errors:
IndexOutOfRangeException: Array index is out of range.
UnityEditor.Graphs.AnimatorControllerTool.ResetBreadCrumbs () (at C:/buildslave/unity/build/Editor/Graphs/UnityEditor.Graphs/Animation/AnimatorControllerTool.cs:441)
UnityEditor.Graphs.AnimatorControllerTool.ResetUI () (at C:/buildslave/unity/build/Editor/Graphs/UnityEditor.Graphs/Animation/AnimatorControllerTool.cs:417)
UnityEditor.Graphs.LayerControllerView.get_selectedLayerIndex () (at C:/buildslave/unity/build/Editor/Graphs/UnityEditor.Graphs/Animation/LayerControllerView.cs:27)
UnityEditor.Graphs.LayerControllerView.ResetUI () (at C:/buildslave/unity/build/Editor/Graphs/UnityEditor.Graphs/Animation/LayerControllerView.cs:139)
UnityEditor.Graphs.AnimatorControllerTool.set_animatorController (UnityEditor.Animations.AnimatorController value) (at C:/buildslave/unity/build/Editor/Graphs/UnityEditor.Graphs/Animation/AnimatorControllerTool.cs:51)
UnityEditor.Graphs.AnimatorControllerTool.DetectAnimatorControllerFromSelection () (at C:/buildslave/unity/build/Editor/Graphs/UnityEditor.Graphs/Animation/AnimatorControllerTool.cs:254)
UnityEditor.Graphs.AnimatorControllerTool.OnEnable () (at C:/buildslave/unity/build/Editor/Graphs/UnityEditor.Graphs/Animation/AnimatorControllerTool.cs:264)
UnityEditor.DockArea:OnGUI()

NullReferenceException: Object reference not set to an instance of an object
UnityEditor.Graphs.LayerControllerView.OnEvent () (at C:/buildslave/unity/build/Editor/Graphs/UnityEditor.Graphs/Animation/LayerControllerView.cs:435)
UnityEditor.Graphs.AnimatorControllerTool.OnGUIEditor (Rect editorRect) (at C:/buildslave/unity/build/Editor/Graphs/UnityEditor.Graphs/Animation/AnimatorControllerTool.cs:620)
UnityEditor.Graphs.AnimatorControllerTool.OnGUI () (at C:/buildslave/unity/build/Editor/Graphs/UnityEditor.Graphs/Animation/AnimatorControllerTool.cs:732)
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)

This might be happening as the animation controller got corrupted. Corruption appears to be random, however, the errors can be seen everytime when trying to open a corrupted controller.