pointerId property Null safety

1. Flutter
2. dart:html
3. PointerEvent
4. pointerId property

PointerEvent class

1. Constructors
2. PointerEvent
3. Properties
4. altKey
5. bubbles
6. button
7. buttons
8. cancelable
9. client
10. composed
11. ctrlKey
12. currentTarget
13. dataTransfer
14. defaultPrevented
15. detail
16. eventPhase
17. fromElement
18. hashCode
19. height
20. isPrimary
21. isTrusted
22. layer
23. matchingTarget
24. metaKey
25. movement
26. offset
27. page
28. path
29. pointerId
30. pointerType
31. pressure
32. region
33. relatedTarget
34. runtimeType
35. screen
36. shiftKey
37. sourceCapabilities
38. tangentialPressure
39. target
40. tiltX
41. tiltY
42. timeStamp
43. toElement
44. twist
45. type
46. view
47. width
48. Methods
49. composedPath
50. getCoalescedEvents
51. getModifierState
52. noSuchMethod
53. preventDefault
54. stopImmediatePropagation
55. stopPropagation
56. toString
57. Operators
58. operator ==
59. Static properties
60. supported