BoxFit constructor Null safety

1. flutter_json_widgets
2. enums
3. BoxFit
4. BoxFit const constructor

BoxFit enum

1. Constructors
2. BoxFit
3. Values
4. fill
5. contain
6. cover
7. fitWidth
8. fitHeight
9. none
10. scaleDown
11. Properties
12. hashCode
13. index
14. runtimeType
15. Methods
16. noSuchMethod
17. toString
18. Operators
19. operator ==
20. Constants
21. values