ChangeNotifier constructor Null safety

1. Flutter
2. foundation
3. ChangeNotifier
4. ChangeNotifier constructor

ChangeNotifier class

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