fix

[maxzod]

New Pull Request Checklist

• I have read the Documentation
• I have searched for a similar pull request in the project and found none
• I have updated this branch with the latest master to avoid conflicts (via merge from master or rebase)
• I have added the required tests to prove the fix/feature I am adding
• I have updated the documentation (if necessary)
• I have run the tests and they pass

This merge request fixes / refers to the following issues: ...
if you declare the request data type final res = await Dio().get<T>(....);
it returns nullable object T? but i have specifically told it it is not nullable when i need to be nullable i will use T? instead

this PR fixes this issues

[NicolaVerbeeck]

Does this PR also fix the case where T is nullable, this has been broken since 4.0.1 (wrong non-null cast in dio_mixin's assureResponse)

[maxzod]

@NicolaVerbeeck yes

[kuhnroyal]

Not sure this is the right approach. In any case, this is a breaking change as it is now required to specify T? for everything that previously worked.

[kuhnroyal]

While I like the idea of explicitly specifying if the response is nullable, this will be a breaking change.
We can consider this for a 5.0.0 release if there is a general consensus. I started a discussion for this: #1335

@NicolaVerbeeck The T? problem has been fixed in #1322