NullReferenceException in unity?

Question

Unity

Performed various operations with prefabs, when I started to bring everything back, the unit throws:

NullReferenceException: Object reference not set to an instance of an object
UnityEditor.Graphs.Edge.WakeUp () (at: 0)
UnityEditor.Graphs.Graph.DoWakeUpEdges ( System.Collections.Generic.List`1[T] inEdges, System.Collections.Generic.List`1[T] ok, System.Collections.Generic.List`1[T] error, System.Boolean inEdgesUsedToBeValid) (at : 0)
UnityEditor.Graphs.Graph.WakeUpEdges (System.Boolean clearSlotEdges) (at :0)
UnityEditor.Graphs.Graph.WakeUp (System.Boolean force) (at :0)
UnityEditor.Graphs.Graph.WakeUp () (at : 0)
UnityEditor.Graphs.Graph.OnEnable() (at :0)

How to understand exactly where the problem is? everywhere, it seems, links to objects and scripts are affixed and the values ​​​​are indicated, I don’t understand what he swears at