Bug Hierarchy turned to a black box.

That black box above used to be my hierarchy. How can I get rid of it?

This happens after I downloaded an animation pack asset that corrupted my manifest.json file (I got loads of errors, none of my other installed assets were working). I replaced my manifest.json file with a file from another project, which sorted out all of my problems, but caused this one.

The errors below are all (I think) related to not being able to load the Hierarchy scene.

I can create a new Hierarchy that works fine.

Unity version is 2019.4.1f1

 

I tried with a "Reimport all" but made no difference.

The error code related to the black box;

NullReferenceException: Object reference not set to an instance of an object

UnityEditor.HostView.DeregisterSelectedPane (System.Boolean clearActualView, System.Boolean sendEvents) (at <a0a9ad37e16b4f7cb955e1101b72d4cc>:0)

UnityEditor.HostView.SetActualViewInternal (UnityEditor.EditorWindow value, System.Boolean sendEvents) (at <a0a9ad37e16b4f7cb955e1101b72d4cc>:0)

UnityEditor.HostView.set_actualView (UnityEditor.EditorWindow value) (at <a0a9ad37e16b4f7cb955e1101b72d4cc>:0)

UnityEditor.DockArea.OnEnable () (at <a0a9ad37e16b4f7cb955e1101b72d4cc>:0)

UnityEditorInternal.InternalEditorUtility:LoadSerializedFileAndForget(String)

UnityEditor.WindowLayout:LoadDefaultWindowPreferences()

 

Assuming you've already restarted Unity, I'd use Window -> Layouts -> Reset Factory Settings.

 

Thank you thank THANK YOU!
I searched low and high for a button like that, but could not find it. Thanks!