UserState constructor Null safety

1. farmershands
2. user_state
3. UserState
4. UserState constructor

UserState class

1. Constructors
2. UserState
3. Properties
4. currentUser
5. doctors
6. hashCode
7. hasListeners
8. runtimeType
9. Methods
10. addListener
11. dispose
12. noSuchMethod
13. notifyListeners
14. removeListener
15. toString
16. Operators
17. operator ==