onSubmit property Null safety

1. baguette
2. BankCardFormWidget
3. BankCardFormWidget
4. onSubmit property

BankCardFormWidget class

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