message property Null safety

1. netease_roomkit
2. netease_roomkit
3. NERoomChatMessage
4. message property

NERoomChatMessage class

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