ProductRefresher constructor Null safety

1. smooth_app
2. product_refresher
3. ProductRefresher
4. ProductRefresher constructor

ProductRefresher class

1. Constructors
2. ProductRefresher
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. noSuchMethod
8. saveAndRefresh
9. toString
10. Operators
11. operator ==