UnreadItemKey constructor Null safety

1. sendbird_sdk
2. enums
3. UnreadItemKey
4. UnreadItemKey const constructor

UnreadItemKey enum

1. Constructors
2. UnreadItemKey
3. Values
4. nonSuperGroupChannelUnreadMessageCount
5. superGroupChannelUnreadMessageCount
6. groupChannelUnreadMessageCount
7. nonSuperGroupChannelUnreadMentionCount
8. superGroupChannelUnreadMentionCount
9. groupChannelUnreadMentionCount
10. nonSuperGroupChannelInvitationCount
11. superGroupChannelInvitationCount
12. groupChannelInvitationCount
13. Properties
14. hashCode
15. index
16. runtimeType
17. Methods
18. noSuchMethod
19. toString
20. Operators
21. operator ==
22. Constants
23. values