isComposing property Null safety

1. Dart
2. dart:html
3. KeyboardEvent
4. isComposing property

KeyboardEvent class

1. Constructors
2. KeyboardEvent
3. Properties
4. altKey
5. bubbles
6. cancelable
7. charCode
8. code
9. composed
10. ctrlKey
11. currentTarget
12. defaultPrevented
13. detail
14. eventPhase
15. hashCode
16. isComposing
17. isTrusted
18. key
19. keyCode
20. location
21. matchingTarget
22. metaKey
23. path
24. repeat
25. runtimeType
26. shiftKey
27. sourceCapabilities
28. target
29. timeStamp
30. type
31. view
32. which
33. Methods
34. composedPath
35. getModifierState
36. noSuchMethod
37. preventDefault
38. stopImmediatePropagation
39. stopPropagation
40. toString
41. Operators
42. operator ==
43. Constants
44. DOM_KEY_LOCATION_LEFT
45. DOM_KEY_LOCATION_NUMPAD
46. DOM_KEY_LOCATION_RIGHT
47. DOM_KEY_LOCATION_STANDARD