CustomCacheManager constructor Null safety

1. appmayor
2. cache_manager
3. CustomCacheManager
4. CustomCacheManager constructor

CustomCacheManager class

1. Constructors
2. CustomCacheManager
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. noSuchMethod
8. toString
9. Operators
10. operator ==
11. Static properties
12. instance
13. Constants
14. key