used property Null safety

1. nertc
2. nertc
3. NERtcStats
4. used property

NERtcStats class

1. Constructors
2. fromMap
3. Properties
4. cpuAppUsage
5. cpuTotalUsage
6. hashCode
7. memory
8. memoryAppUsageInKBytes
9. memoryAppUsageRatio
10. memoryTotalUsageRatio
11. runtimeType
12. rxAudioBytes
13. rxAudioJitter
14. rxAudioKBitRate
15. rxAudioPacketLossRate
16. rxAudioPacketLossSum
17. rxBytes
18. rxVideoBytes
19. rxVideoJitter
20. rxVideoKBitRate
21. rxVideoPacketLossRate
22. rxVideoPacketLossSum
23. the
24. totalDuration
25. txAudioBytes
26. txAudioJitter
27. txAudioKBitRate
28. txAudioPacketLossRate
29. txAudioPacketLossSum
30. txBytes
31. txVideoBytes
32. txVideoJitter
33. txVideoKBitRate
34. txVideoPacketLossRate
35. txVideoPacketLossSum
36. upRtt
37. used
38. Methods
39. app
40. noSuchMethod
41. toString
42. Operators
43. operator *
44. operator ==