CommandType constructor Null safety

1. sendbird_sdk
2. command_type
3. CommandType
4. CommandType const constructor

CommandType enum

1. Constructors
2. CommandType
3. Values
4. userMessage
5. userMessageUpdate
6. fileMessage
7. fileMessageUpdate
8. adminMessage
9. adminMessageUpdate
10. broadcastMessage
11. deleteMessage
12. delivery
13. read
14. memberCountChange
15. reaction
16. threading
17. userEvent
18. systemEvent
19. sessionExpired
20. error
21. login
22. enter
23. exit
24. mack
25. typingStart
26. typingEnd
27. ping
28. pollVote
29. pollUpdate
30. Properties
31. hashCode
32. index
33. runtimeType
34. Methods
35. noSuchMethod
36. toString
37. Operators
38. operator ==
39. Constants
40. values