NERoomChatCustomMessage constructor Null safety

1. netease_roomkit
2. netease_roomkit
3. NERoomChatCustomMessage
4. NERoomChatCustomMessage constructor

NERoomChatCustomMessage class

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