1. Add LODGroup component to Main Camera.
2. In Inspector panel for LODGroup select any group. e.g. LOD: 1
3. Press button Add to add renderer
4. In popuped window select None.

You'll get
NullReferenceException: Object reference not set to an instance of an object
UnityEditor.LODGroupEditor <GetRenderers>c__AnonStorey50.<>m__B4 (UnityEngine.GameObject go) (at C:/BuildAgent/work/afa2580bf6048259/Editor/Mono/Inspector/LODGroupEditor.cs:559)
System.Linq.Enumerable <CreateWhereIterator>c__Iterator1D`1[UnityEngine.GameObject].MoveNext ()
System.Linq.Enumerable.Count[GameObject] (IEnumerable`1 source)
UnityEditor.LODGroupEditor.GetRenderers (IEnumerable`1 selectedGameObjects, Boolean searchChildren) (at C:/BuildAgent/work/afa2580bf6048259/Editor/Mono/Inspector/LODGroupEditor.cs:564)