bankCard property Null safety

1. baguette
2. BankCardWidget
3. BankCardWidget
4. bankCard property

BankCardWidget class

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