reverse method Null safety

1. Flutter
2. dart:html
3. Animation
4. reverse method

Animation class

1. Constructors
2. Animation
3. Properties
4. currentTime
5. effect
6. finished
7. hashCode
8. id
9. on
10. onCancel
11. onFinish
12. playbackRate
13. playState
14. ready
15. runtimeType
16. startTime
17. timeline
18. Methods
19. addEventListener
20. cancel
21. dispatchEvent
22. finish
23. noSuchMethod
24. pause
25. play
26. removeEventListener
27. reverse
28. toString
29. Operators
30. operator ==
31. Static properties
32. supported
33. Constants
34. cancelEvent
35. finishEvent