ChannelEventHandler constructor Null safety

1. sendbird_sdk
2. channel_event_handler
3. ChannelEventHandler
4. ChannelEventHandler constructor

ChannelEventHandler class

1. Constructors
2. ChannelEventHandler
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. noSuchMethod
8. onChannelChanged
9. onChannelDeleted
10. onChannelFrozen
11. onChannelHidden
12. onChannelMemberCountChanged
13. onChannelOperatorsUpdated
14. onChannelParticipantCountChanged
15. onChannelUnfrozen
16. onDeliveryReceiptUpdated
17. onMentionReceived
18. onMessageDeleted
19. onMessageReceived
20. onMessageUpdated
21. onMetaCountersCreated
22. onMetaCountersDeleted
23. onMetaCountersUpdated
24. onMetaDataCreated
25. onMetaDataDeleted
26. onMetaDataUpdated
27. onPinUpdated
28. onPollDeleted
29. onPollUpdated
30. onPollVoted
31. onReactionUpdated
32. onReadReceiptUpdated
33. onThreadInfoUpdated
34. onTypingStatusUpdated
35. onUserBanned
36. onUserDeclinedInvitation
37. onUserEntered
38. onUserExited
39. onUserJoined
40. onUserLeaved
41. onUserMuted
42. onUserReceivedInvitation
43. onUserUnbanned
44. onUserUnmuted
45. toString
46. Operators
47. operator ==