open constant Null safety

1. Flutter
2. dart:io
3. WebSocket
4. open constant

WebSocket class

1. Constructors
2. WebSocket
3. fromUpgradedSocket
4. Properties
5. closeCode
6. closeReason
7. done
8. extensions
9. first
10. hashCode
11. isBroadcast
12. isEmpty
13. last
14. length
15. pingInterval
16. protocol
17. readyState
18. runtimeType
19. single
20. Methods
21. add
22. addError
23. addStream
24. addUtf8Text
25. any
26. asBroadcastStream
27. asyncExpand
28. asyncMap
29. cast
30. close
31. contains
32. distinct
33. drain
34. elementAt
35. every
36. expand
37. firstWhere
38. fold
39. forEach
40. handleError
41. join
42. lastWhere
43. listen
44. map
45. noSuchMethod
46. pipe
47. reduce
48. singleWhere
49. skip
50. skipWhile
51. take
52. takeWhile
53. timeout
54. toList
55. toSet
56. toString
57. transform
58. where
59. Operators
60. operator ==
61. Static properties
62. userAgent
63. Static methods
64. connect
65. Constants
66. closed
67. closing
68. connecting
69. open