child property Null safety

1. baguette
2. BlockWidget
3. BlockWidget
4. child property

BlockWidget class

1. Constructors
2. BlockWidget
3. Properties
4. child
5. hashCode
6. key
7. mode
8. runtimeType
9. Methods
10. build
11. createElement
12. debugDescribeChildren
13. debugFillProperties
14. noSuchMethod
15. toDiagnosticsNode
16. toString
17. toStringDeep
18. toStringShallow
19. toStringShort
20. Operators
21. operator ==