NEMessageChannelService constructor Null safety

1. netease_roomkit
2. netease_roomkit
3. NEMessageChannelService
4. NEMessageChannelService constructor

NEMessageChannelService class

1. Constructors
2. NEMessageChannelService
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. addMessageChannelCallback
8. noSuchMethod
9. removeMessageChannelCallback
10. sendCustomMessage
11. toString
12. Operators
13. operator ==