margin property Null safety

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

MessageWidget class

1. Constructors
2. MessageWidget
3. Properties
4. conversation
5. hashCode
6. key
7. margin
8. message
9. onActions
10. onPress
11. padding
12. runtimeType
13. Methods
14. createElement
15. createState
16. debugDescribeChildren
17. debugFillProperties
18. noSuchMethod
19. toDiagnosticsNode
20. toString
21. toStringDeep
22. toStringShallow
23. toStringShort
24. Operators
25. operator ==