NullReferenceException Using Animator

I’m trying to use the Animator to control my sprite animations. I have set up the animations, but when I place them in the animator, and the Animator in the Character, I get this error. It doesn’t do anything. But I have no clue how to remove it.

NullReferenceException: (null)
UnityEditor.SerializedObject..ctor (UnityEngine.Object obj) (at 
    UnityEditor.Graphs.AnimationStateMachine.TransitionInspector.SetTransitionToInspect (UnityEditorInternal.Transition transition) (at C:/BuildAgent/work/d3d49558e4d408f4/Editor/Graphs/UnityEditor.Graphs/AnimationStateMachine/TransitionInspector.cs:173)
    UnityEditor.Graphs.AnimationStateMachine.TransitionInspector.OnEnable () (at C:/BuildAgent/work/d3d49558e4d408f4/Editor/Graphs/UnityEditor.Graphs/AnimationStateMachine/TransitionInspector.cs:96)

Ha - get that too - I think because I deleted the initial animation controller created when i dragged some frames across to the stage, and created my own blank one to drag animations into.

I can’t fix it either - this animation set-up is just hilarious eh ?