extraInfo property Null safety

1. wings_data_model
2. wings_data_model
3. ContentElement
4. extraInfo property

ContentElement class

1. Constructors
2. ContentElement
3. Properties
4. address
5. applicableConditions
6. applicableCountries
7. applicableInterests
8. city
9. coordinates
10. country
11. description
12. extraInfo
13. hashCode
14. hero
15. heroVideo
16. id
17. isLiked
18. locale
19. name
20. originator
21. province
22. runtimeType
23. subtitle
24. title
25. type
26. zipCode
27. Methods
28. noSuchMethod
29. rebuild
30. toBuilder
31. toString
32. Operators
33. operator ==