Unable to return Null/None in a custom Scalar type

[Emmet McPoland]

Attempting to return None if the image is a blank string

class Image(graphene.types.Scalar):

    @staticmethod
    def serialize(image):
        return image.url if image else None

    @staticmethod
    def parse_literal(node):
        return None

    @staticmethod
    def parse_value(value):
        return None

but am receiving the following error

graphql.error.base.GraphQLError: Expected a value of type "Image" but received:

Going by the comment at https://github.com/graphql-python/graphql-core/blob/master/graphql/execution/executor.py#L615 this should be possible, however the code does not imply that its possible.

There appears to be PRs for this feature (By adding an explicit NullValue)
graphql-python/graphql-core#119
graphql-python/graphql-core#172

But it appears this issue isn't gonna be fixed until graphql-core-next is released. Ive attempted to install the next alpha version along with graphene-django but it seems unhappy. (Are they currently incompatible)?

[Emmet McPoland]

Ended up having to monkey patch it

# Allow None to be returned in type serialiser
from graphql.execution import executor
def patched_complete_leaf_value(return_type, path, result):
    assert hasattr(return_type, "serialize"), "Missing serialize method on type"
    serialized_result = return_type.serialize(result)
    return serialized_result
executor.complete_leaf_value = patched_complete_leaf_value

[Emmet McPoland]

Also regarding graphene-django and django-core v3. I just saw this post graphql-python/graphene-django#705

Looks like it will be coming in the near future.

[Emmet McPoland]

Another way to do it is in the resolver thats passed to the field. No monkey patch required.

from graphene.utils.str_converters import to_snake_case
def ResolveNoneIfEmpty(instance, info):
    field_name = to_snake_case(info.field_name)
    field_value = getattr(instance, field_name)
    return field_value if field_value else None
NullEmptyString = lambda *args, **kwargs : graphene.String(*args, **kwargs, resolver=ResolveNoneIfEmpty)

class Member(DjangoObjectType):
    ....
    display_name = NullEmptyString()