fit property Null safety

1. flutter_json_widgets
2. widget
3. Image
4. fit property

Image class

1. Constructors
2. Image
3. fromJson
4. Properties
5. alignment
6. centerSlice
7. color
8. colorBlendMode
9. copyWith
10. excludeFromSemantics
11. filterQuality
12. fit
13. gaplessPlayback
14. hashCode
15. height
16. image
17. isAntiAlias
18. key
19. matchTextDirection
20. repeat
21. runtimeType
22. semanticLabel
23. width
24. Methods
25. map
26. mapOrNull
27. maybeMap
28. maybeWhen
29. noSuchMethod
30. toJson
31. toString
32. when
33. whenOrNull
34. Operators
35. operator ==