HyperlinkRelated creating invalid endpoint

Nobody has claimed this yet.

For some reason HyperlinkRelated seems to create an invalid endpoint with HyperlinkRelated which Flask rejects:

`Exception has occurred: BuildError (note: full exception trace is shown but execution is paused at: api_GetMagazine)
Could not build url for endpoint '/api/publishers' with values ['id']. Did you mean 'publishers' instead?`

These are my models:
```
class MagazineSchema(ma.SQLAlchemySchema):
class Meta:
model = Magazine
id = ma.auto_field()
name = ma.auto_field()
publisher = ma.HyperlinkRelated(
endpoint='/api/publishers')
```

```
class PublisherSchema(ma.SQLAlchemySchema):
class Meta:
model = Publisher
id = ma.auto_field()
```

And this is what that API looks like:
```
@app.route('/api/publishers/', methods=['get'])
def api_GetPublisher(id: Any) -> Any:
options = {}
options['publisherId'] = id
return GetPublisher(options)
```

This API works with curl.

And this is how I try to dump the results in GetPublisher:
```
schema = MagazineSchema()
retval = schema.dump(magazine)
```

Am I doing something wrong? I can't figure out what that could be. I tried both with AutoSchema and Schema and both give the same result.

Start by reading HyperlinkRelated in the schema definitions and compare its endpoint handling with the api_GetPublisher route shown in the issue. Reproduce the schema.dump(magazine) call and inspect the generated endpoint name and URL values. Done means dumping a magazine produces a valid publisher hyperlink accepted by Flask.

Written by the indexing model from the issue text.