appBar property Null safety

1. flutter_json_widgets
2. widget
3. Scaffold
4. appBar property

Scaffold class

1. Constructors
2. Scaffold
3. fromJson
4. Properties
5. appBar
6. backgroundColor
7. body
8. bottomNavigationBar
9. bottomSheet
10. copyWith
11. drawer
12. drawerEdgeDragWidth
13. drawerEnableOpenDragGesture
14. drawerScrimColor
15. endDrawer
16. endDrawerEnableOpenDragGesture
17. extendBody
18. extendBodyBehindAppBar
19. floatingActionButton
20. floatingActionButtonLocation
21. hashCode
22. key
23. persistentFooterAlignment
24. persistentFooterButtons
25. primary
26. resizeToAvoidBottomInset
27. restorationId
28. runtimeType
29. Methods
30. map
31. mapOrNull
32. maybeMap
33. maybeWhen
34. noSuchMethod
35. toJson
36. toString
37. when
38. whenOrNull
39. Operators
40. operator ==