Peewee and Flask-Admin: View with only foreign keys missing attribute '_data'

I use flask peewee together with flask-admin and it works fine for some model classes, but I got one model, that it does not work on and gives me the following error:

AttributeError: 'GroupMember' object has no attribute '_data'

This is how the model looks:

class GroupMember(BaseModel):
   group = ForeignKeyField(Group)
   member = ForeignKeyField(Member)

    class Meta:
        primary_key = CompositeKey('group', 'member')

As this model consists of only foreign keys, I thought I would need to create a custom view that lists the columns explicitly, because by default flask-admin hides those columns.

I did so:

class MyModelView(ModelView):
    column_list = ('group', 'member')

And initialized the view: admin.add_view(MyModelView(GroupMember))

This honestly changed nothing and I still get the same error. I found related questions that mentioned "backrefs" - what would that do and how would I do this? Or is this even the reason for my problem?

from Peewee and Flask-Admin: View with only foreign keys missing attribute '_data'