Using flatten inside an impl with no other fields causes a compile error

[bbqsrc]

Expected Behavior

Using flatten on a struct without any other fields should work, as it used to. This is a regression. And yes I know that this pattern is strange but I have good reasons to be using it, haha.

Actual Behavior

It gives an error now:

error: A GraphQL Object type must define one or more fields.

Steps to Reproduce the Problem

#[derive(Debug, SimpleObject)]
pub struct Inner {
    pub foo: String
}

pub struct Foo;

#[Object]
impl Foo {
    #[graphql(flatten)]
    async fn _inner(&self) -> Inner {
        Inner {
            foo: "bar".to_string()
        }
    }
}

Specifications

• Version: 7.0.2
• Platform: macos