NERoomMessage constructor Null safety

1. yunxin_roomkit
2. roomkit
3. NERoomMessage
4. NERoomMessage constructor

NERoomMessage class

1. Constructors
2. NERoomMessage
3. Properties
4. fromAccount
5. fromNick
6. hashCode
7. messageType
8. runtimeType
9. time
10. toAccounts
11. Methods
12. noSuchMethod
13. toString
14. Operators
15. operator ==