ProductQuery constructor Null safety

1. smooth_app
2. product_query
3. ProductQuery
4. ProductQuery constructor

ProductQuery class

1. Constructors
2. ProductQuery
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. getProductList
8. getSearchResult
9. noSuchMethod
10. toString
11. Operators
12. operator ==
13. Static properties
14. fields
15. Static methods
16. getCountry
17. getLanguage
18. getLocaleString
19. getUser
20. setCountry
21. setLanguage
22. setQueryType
23. setUuid