KeepAliveHandle constructor Null safety

1. Flutter
2. widgets
3. KeepAliveHandle
4. KeepAliveHandle constructor

KeepAliveHandle class

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