Substituted_Kind constructor Null safety

1. spine_client
2. command_log.pb
3. Substituted_Kind
4. Substituted_Kind const constructor

Substituted_Kind enum

1. Constructors
2. Substituted_Kind
3. Values
4. command
5. sequence
6. notSet
7. Properties
8. hashCode
9. index
10. runtimeType
11. Methods
12. noSuchMethod
13. toString
14. Operators
15. operator ==
16. Constants
17. values