PreviousFocusAction constructor Null safety

1. Flutter
2. widgets
3. PreviousFocusAction
4. PreviousFocusAction constructor

PreviousFocusAction class

1. Constructors
2. PreviousFocusAction
3. Properties
4. callingAction
5. hashCode
6. intentType
7. isActionEnabled
8. runtimeType
9. Methods
10. addActionListener
11. consumesKey
12. debugFillProperties
13. invoke
14. isEnabled
15. noSuchMethod
16. notifyActionListeners
17. removeActionListener
18. toDiagnosticsNode
19. toString
20. toStringShort
21. Operators
22. operator ==