onFetch property Null safety

1. baguette
2. ConversationListWidget
3. ConversationListWidget
4. onFetch property

ConversationListWidget class

1. Constructors
2. ConversationListWidget
3. Properties
4. hashCode
5. isArchives
6. itemMargin
7. itemPadding
8. key
9. margin
10. onActions
11. onFetch
12. onPress
13. onWrite
14. padding
15. runtimeType
16. Methods
17. createElement
18. createState
19. debugDescribeChildren
20. debugFillProperties
21. noSuchMethod
22. toDiagnosticsNode
23. toString
24. toStringDeep
25. toStringShallow
26. toStringShort
27. Operators
28. operator ==