color property Null safety

1. flutter_json_widgets
2. widget
3. Divider
4. color property

Divider class

1. Constructors
2. Divider
3. fromJson
4. Properties
5. color
6. copyWith
7. endIndent
8. hashCode
9. height
10. indent
11. key
12. runtimeType
13. thickness
14. Methods
15. map
16. mapOrNull
17. maybeMap
18. maybeWhen
19. noSuchMethod
20. toJson
21. toString
22. when
23. whenOrNull
24. Operators
25. operator ==