RecordState constructor Null safety

1. nim_core
2. nim_core
3. RecordState
4. RecordState const constructor

RecordState enum

1. Constructors
2. RecordState
3. Values
4. READY
5. START
6. REACHED_MAX
7. SUCCESS
8. FAIL
9. CANCEL
10. Properties
11. hashCode
12. index
13. runtimeType
14. Methods
15. noSuchMethod
16. toString
17. Operators
18. operator ==
19. Constants
20. values