leadingWidth property Null safety

1. flutter_json_widgets
2. sliver
3. SliverAppBarMedium
4. leadingWidth property

SliverAppBarMedium class

1. Constructors
2. SliverAppBarMedium
3. fromJson
4. Properties
5. actions
6. automaticallyImplyLeading
7. backgroundColor
8. bottom
9. centerTitle
10. collapsedHeight
11. copyWith
12. elevation
13. excludeHeaderSemantics
14. expandedHeight
15. flexibleSpace
16. floating
17. forceElevated
18. foregroundColor
19. hashCode
20. key
21. leading
22. leadingWidth
23. pinned
24. primary
25. runtimeType
26. scrolledUnderElevation
27. shadowColor
28. shape
29. snap
30. stretch
31. stretchTriggerOffset
32. surfaceTintColor
33. title
34. titleSpacing
35. titleTextStyle
36. toolbarHeight
37. toolbarTextStyle
38. Methods
39. map
40. mapOrNull
41. maybeMap
42. maybeWhen
43. noSuchMethod
44. toJson
45. toString
46. when
47. whenOrNull
48. Operators
49. operator ==