[Solved]unexplanable null refrence exception

so i was working with animation for the first time today using it to animate part of a (4.5) UI. and at one point (really not sure when) i started getting this nullref error. it doesn’t seem to do anything…but its there and it worries me that it could be hurting something in the background. i have no scripts for this animation its 100% done with the editor (animation editor and the animation node editor)
heres the stack trace. maybe someone can help me figure out what’s causing it so i can put a stop to it

(p.s. : i completely removed the animation controller from the game object and this was still happening so i really don’t know right now why this is a thing)

NullReferenceException: Object reference not set to an instance of an object
UnityEditor.Graphs.AnimationStateMachine.TransitionEditionContext.BuildNames () (at C:/buildslave/unity/build/Editor/Graphs/UnityEditor.Graphs/AnimationStateMachine/TransitionEditionContext.cs:44)
UnityEditor.Graphs.AnimationStateMachine.TransitionEditionContext..ctor (UnityEditor.Animations.AnimatorTransitionBase aTransition, UnityEditor.Animations.AnimatorState aSourceState, UnityEditor.Animations.AnimatorStateMachine aSourceStateMachine, UnityEditor.Animations.AnimatorStateMachine aOwnerStateMachine) (at C:/buildslave/unity/build/Editor/Graphs/UnityEditor.Graphs/AnimationStateMachine/TransitionEditionContext.cs:28)
UnityEditor.Graphs.AnimationStateMachine.AnimatorTransitionInspectorBase.ComputeTransitionContexts () (at C:/buildslave/unity/build/Editor/Graphs/UnityEditor.Graphs/AnimationStateMachine/AnimatorTransitionInspectorBase.cs:125)
UnityEditor.Graphs.AnimationStateMachine.AnimatorTransitionInspectorBase.OnEnable () (at C:/buildslave/unity/build/Editor/Graphs/UnityEditor.Graphs/AnimationStateMachine/AnimatorTransitionInspectorBase.cs:87)
UnityEditor.Graphs.AnimationStateMachine.AnimatorStateTransitionInspector.OnEnable () (at C:/buildslave/unity/build/Editor/Graphs/UnityEditor.Graphs/AnimationStateMachine/AnimatorStateTransitionInspector.cs:58)

Had to restart unity! thanks to zach.r.d and Positive7 for the tip!!!

Yeah try restarting Unity. Sonewhat inexplicable null reference voids occur in 4.5. These do not persist after the game is compiled.

just save your current layout, it should solve your error,

I found my Animation Play, Pause and Next Frame buttons were Red suggesting the animation was still trying to record key frames.
Once I turned these off (by pressing the red play button again - the one that normally enters the play game mode) I was able to continue as before.