ChatType constructor Null safety

1. agora_chat_sdk
2. agora_chat_sdk
3. ChatType
4. ChatType const constructor

ChatType enum

1. Constructors
2. ChatType
3. Values
4. Chat
5. GroupChat
6. ChatRoom
7. Properties
8. hashCode
9. index
10. runtimeType
11. Methods
12. noSuchMethod
13. toString
14. Operators
15. operator ==
16. Constants
17. values