Impossibility to set InputSystemUIInputModule.localMultiPlayerRoot to null

Steps to reproduce:

1. assign a MultiplayerEventSystem.playerRoot to a value
2. try assigning null
3. observe the hierarchy restriction value

Actual results: 
the playerRoot can not be set to null

Expected results: 
the playerRoot can be set to null

Reproducible with versions: 1.14.0

Notes: