AbstractNode constructor Null safety

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

AbstractNode class

1. Constructors
2. AbstractNode
3. Properties
4. attached
5. depth
6. hashCode
7. owner
8. parent
9. runtimeType
10. Methods
11. adoptChild
12. attach
13. detach
14. dropChild
15. noSuchMethod
16. redepthChild
17. redepthChildren
18. toString
19. Operators
20. operator ==