client property Null safety

1. wings_data_model
2. wings_data_model
3. DioLink
4. client property

DioLink class

1. Constructors
2. DioLink
3. Properties
4. client
5. defaultHeaders
6. endpoint
7. hashCode
8. parser
9. runtimeType
10. serializer
11. Methods
12. close
13. concat
14. dispose
15. noSuchMethod
16. request
17. route
18. split
19. toString
20. Operators
21. operator ==