margin property Null safety

1. baguette
2. BoxWidget
3. BoxWidget
4. margin property

BoxWidget class

1. Constructors
2. BoxWidget
3. Properties
4. axis
5. borderColor
6. borderRadius
7. borderShadow
8. color
9. hashCode
10. height
11. image
12. info
13. key
14. label
15. margin
16. onPress
17. padding
18. runtimeType
19. visibility
20. width
21. Methods
22. build
23. createElement
24. debugDescribeChildren
25. debugFillProperties
26. noSuchMethod
27. toDiagnosticsNode
28. toString
29. toStringDeep
30. toStringShallow
31. toStringShort
32. Operators
33. operator ==