NERoomTextMessage constructor Null safety

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

NERoomTextMessage class

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