DownloadErrorCode constructor Null safety

1. mapbox_maps_flutter
2. mapbox_maps_flutter
3. DownloadErrorCode
4. DownloadErrorCode const constructor

DownloadErrorCode enum

1. Constructors
2. DownloadErrorCode
3. Values
4. FILE_SYSTEM_ERROR
5. NETWORK_ERROR
6. Properties
7. hashCode
8. index
9. runtimeType
10. Methods
11. noSuchMethod
12. toString
13. Operators
14. operator ==
15. Constants
16. values