SubscriptionUpdate_Update constructor Null safety

1. spine_client
2. subscription.pb
3. SubscriptionUpdate_Update
4. SubscriptionUpdate_Update const constructor

SubscriptionUpdate_Update enum

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