goBackward method Null safety

1. baguette
2. WebWidget
3. WebWidget
4. goBackward method

WebWidget class

1. Constructors
2. WebWidget
3. Properties
4. hashCode
5. key
6. onError
7. onFinish
8. onStart
9. runtimeType
10. uri
11. Methods
12. build
13. canGoBackward
14. canGoForward
15. createElement
16. currentUri
17. debugDescribeChildren
18. debugFillProperties
19. goBackward
20. goForward
21. load
22. noSuchMethod
23. toDiagnosticsNode
24. toString
25. toStringDeep
26. toStringShallow
27. toStringShort
28. Operators
29. operator ==