NERoomChatMessage constructor Null safety

1. netease_roomkit
2. netease_roomkit
3. NERoomChatMessage
4. NERoomChatMessage constructor

NERoomChatMessage class

1. Constructors
2. NERoomChatMessage
3. Properties
4. fromNick
5. fromUserUuid
6. hashCode
7. messageType
8. messageUuid
9. runtimeType
10. time
11. toUserUuidList
12. Methods
13. noSuchMethod
14. toString
15. Operators
16. operator ==