wk constant Null safety

1. wings_data_model
2. wings_data_model
3. TimingCode
4. wk constant

TimingCode class

1. Properties
2. hashCode
3. name
4. runtimeType
5. Methods
6. noSuchMethod
7. toString
8. Operators
9. operator ==
10. Static properties
11. serializer
12. values
13. Static methods
14. valueOf
15. Constants
16. am
17. mo
18. pm
19. qd
20. qod
21. wk