Fix error raised in deserialization of resolver aliased parameters.

[callumforrester]

Fix aliased resolver arguments being looked up by original value when checking for parameter requirement. Unsure if the routine needs to check for both the alias and original parameter name.

[wyfo]

Thank you for having spotted this tricky bug.

Because it's not enough documented in the code, let me explain the reason of this conditional continue. Normally, if the parameter hasn't Optional type, it should result in a non-null parameter in the generated GraphQL schema, and this condition should never be true (because graphql-core would raise an error before calling the resolver). However, there is three cases in which the parameter can become nullable in the schema, which are handled here:

• If the parameter default is Undefined, it should be able to be omitted, and that's only possible with a nullable type, so Optional is added just for the schema generation, but not for deserialization; null/None is thus ignored for this parameter.
• If the parameter default is None with a non-optional type, what is possible because of Python typing rule and a kind of bug in typing.get_type_hints; in this case, Optional is added for the schema generation. However i've just realized that i should have written opt_param = is_union_of(param_type, NoneType) or param.default is None, so opt_param should be true.
• If the serialization of the parameter default fails, it can not be added in the schema, but the field has to be optional, which result in nullable in the schema.
  In all of this cases, parameter has a default value (so it's not required), but the None value is authorized because it has been added as a dummy default, so it's skipped.

Concerning your test, for this kind of issue, i would prefer an "integration test", calling graphql.graphql_sync with a generated schema, but it's up to you, I can merge now.

Unsure if the routine needs to check for both the alias and original parameter name.
Only the alias. This line of code was written at a time were aliases where handled differently, and it had not been updated accordingly when aliases have been added here.

[wyfo]

This comment is not exact (see my comment in the PR)
The parameter is not required but its default is not serializable, so it ends up with an optional parameter, with null as an authorized value. In that case, it should be ignored to ensure using the true default value.

[wyfo]

By the way, because the parameter is in kwargs, that means it has been explicitely supplied by the GraphQL query.

[callumforrester]

I've redone the comment, is that closer to what you mean? Re: kwargs, do you mean as opposed to just having a default value?

[wyfo]

The comment is perfect.
About kwargs, your previous comment was not exact, because kwargs[alias] being None means that the argument *was supplied in the query; if it was not supplied, kwargs would not contains alias.

[callumforrester]

Thanks for taking a look. I agree RE: the tests, I've moved them. I'm also happy to include the correction to opt_param = is_union_of(param_type, NoneType) or param.default is None or I can leave that to you to do in another PR, up to you.

[wyfo]

Concerning opt_param, i will do it in an other PR in order to merge yours directly. I've modified the title of the PR because I use them to generate the changelog.
Thank you a lot for your contribution!