When trying to return union type of custom types, the schema generator fails.

Describe the Bug

Two custom types declared, and one that contains the union of them.

T = TypeVar("T")

@strawberry.type
class MySubType:
    data: str

@strawberry.type
class MySubType2:
    data: int

@strawberry.type
class MyType(Generic[T]):
    data: T


@strawberry.type
class Mutation:

    @strawberry.field
    async def test_mutation(self) -> MyType[Union[MySubType, MySubType2]]:
        return MyType(data=MySubType(data="test"))

The startup fails, with the following traceback:
Traceback (most recent call last):
File "/home/dewitars/.pyenv/versions/3.10.5/envs/fax-api/lib/python3.10/site-packages/graphql/type/definition.py", line 808, in fields
fields = resolve_thunk(self.fields)
File "/home/dewitars/.pyenv/versions/3.10.5/envs/fax-api/lib/python3.10/site-packages/graphql/type/definition.py", line 300, in resolve_thunk
return thunk() if callable(thunk) else thunk
File "/home/dewitars/.pyenv/versions/3.10.5/envs/fax-api/lib/python3.10/site-packages/strawberry/schema/schema_converter.py", line 509, in
fields=lambda: self.get_graphql_fields(object_type),
File "/home/dewitars/.pyenv/versions/3.10.5/envs/fax-api/lib/python3.10/site-packages/strawberry/schema/schema_converter.py", line 373, in get_graphql_fields
return get_thunk_mapping(
File "/home/dewitars/.pyenv/versions/3.10.5/envs/fax-api/lib/python3.10/site-packages/strawberry/schema/schema_converter.py", line 133, in get_thunk_mapping
thunk_mapping[name_converter(field)] = field_converter(
File "/home/dewitars/.pyenv/versions/3.10.5/envs/fax-api/lib/python3.10/site-packages/strawberry/schema/schema_converter.py", line 314, in from_field
self.from_maybe_optional(
File "/home/dewitars/.pyenv/versions/3.10.5/envs/fax-api/lib/python3.10/site-packages/strawberry/schema/schema_converter.py", line 762, in from_maybe_optional
return GraphQLNonNull(self.from_type(type))
File "/home/dewitars/programming/dvrt-graphene-tools/dvrt_graphene_tools/schema.py", line 61, in from_type
return super().from_type(type)
File "/home/dewitars/.pyenv/versions/3.10.5/envs/fax-api/lib/python3.10/site-packages/strawberry/schema/schema_converter.py", line 780, in from_type
return self.from_object(type.strawberry_definition)
File "/home/dewitars/.pyenv/versions/3.10.5/envs/fax-api/lib/python3.10/site-packages/strawberry/schema/schema_converter.py", line 476, in from_object
object_type_name = self.config.name_converter.from_type(object_type)
File "/home/dewitars/.pyenv/versions/3.10.5/envs/fax-api/lib/python3.10/site-packages/strawberry/schema/name_converter.py", line 55, in from_type
return self.from_object(type_)
File "/home/dewitars/.pyenv/versions/3.10.5/envs/fax-api/lib/python3.10/site-packages/strawberry/schema/name_converter.py", line 70, in from_object
return self.from_generic(
File "/home/dewitars/.pyenv/versions/3.10.5/envs/fax-api/lib/python3.10/site-packages/strawberry/schema/name_converter.py", line 136, in from_generic
name = self.get_from_type(type_)
File "/home/dewitars/.pyenv/versions/3.10.5/envs/fax-api/lib/python3.10/site-packages/strawberry/schema/name_converter.py", line 150, in get_from_type
assert type_.graphql_name
AssertionError

But if we are specific, and put the Union in 'MyType', it works just fine:

T = TypeVar("T")

@strawberry.type
class MySubType:
    data: str

@strawberry.type
class MySubType2:
    data: int

@strawberry.type
class MyType:
    data: Union[MySubType, MySubType2]


@strawberry.type
class Mutation:

    @strawberry.field
    async def test_mutation(self) -> MyType:
        return MyType(data=MySubType(data="test"))

System Information

• Operating system: Ubuntu 23.04 x86_64
• Strawberry version (if applicable): 0.195.2

Additional Context

I can not provide the lines that are related to dvrt-graphene-tools (proprietary), but I can ensure that it just calls the strawberry.schema.schema_converter.GraphQLCoreConverter.from_type function with the provided type.