endRoom method Null safety

1. yunxin_roomkit
2. roomkit
3. NERoomContext
4. endRoom abstract method

NERoomContext class

1. Constructors
2. NERoomContext
3. Properties
4. chatController
5. hashCode
6. isRoomLocked
7. liveController
8. localMember
9. password
10. properties
11. remoteMembers
12. roomName
13. roomUuid
14. rtcController
15. rtcStartTime
16. runtimeType
17. whiteboardController
18. Methods
19. addAttachment
20. addEventCallback
21. changeMemberRole
22. changeMyName
23. clearAttachments
24. deleteMemberProperty
25. deleteRoomProperty
26. endRoom
27. getAttachment
28. handOverMyRole
29. kickMemberOut
30. leaveRoom
31. lockRoom
32. noSuchMethod
33. ofMember
34. removeAttachment
35. removeEventCallback
36. toString
37. unlockRoom
38. updateMemberProperty
39. updateRoomProperty
40. Operators
41. operator ==