child property Null safety

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

StripeWidget class

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