avatar property Null safety

1. wings_data_model
2. wings_data_model
3. Organization
4. avatar property

Organization class

1. Constructors
2. Organization
3. Properties
4. address
5. avatar
6. hashCode
7. id
8. name
9. practitionerRoles
10. runtimeType
11. type
12. Methods
13. noSuchMethod
14. rebuild
15. toBuilder
16. toString
17. Operators
18. operator ==