CacheUnit constructor Null safety

1. sendbird_sdk
2. cache_service
3. CacheUnit
4. CacheUnit constructor

CacheUnit class

1. Constructors
2. CacheUnit
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. delete
8. find
9. insert
10. markAsDirty
11. noSuchMethod
12. toString
13. Operators
14. operator ==