Look rotation viewing vector is zero
UnityEngine.Quaternion:Internal_LookRotation (UnityEngine.Vector3&,UnityEngine.Vector3&)
UnityEditorInternal.Slider2D:CalcDeltaAlongDirections (int,UnityEngine.Vector3,UnityEngine.Vector3,UnityEngine.Vector3,UnityEngine.Vector3,UnityEngine.Vector3,single,UnityEditor.Handles/CapFunction,UnityEngine.Vector2,bool) (at /home/bokken/build/output/unity/unity/Editor/Mono/Handles/Slider2D.cs:92)
UnityEditorInternal.Slider2D:Do (int,UnityEngine.Vector3,UnityEngine.Vector3,UnityEngine.Vector3,UnityEngine.Vector3,UnityEngine.Vector3,single,UnityEditor.Handles/CapFunction,UnityEngine.Vector2,bool) (at /home/bokken/build/output/unity/unity/Editor/Mono/Handles/Slider2D.cs:60)
UnityEngine.GUIUtility:ProcessEvent (UnityEngine.EntityId,intptr,bool&)