Unable to set reverse_delte_rule to GenericReferenceField. AttributeError: 'GenericReferenceField' object has no attribute 'document_type'

I get the following error when trying to add "reverse_delete_rule=db.CASCADE" to a GenericReferenceField:

AttributeError: 'GenericReferenceField' object has no attribute 'document_type'

This is my code:

`from database.db import db

class Movie(db.DynamicDocument):
name = db.StringField(required=True, unique=True)
casts = db.ListField(db.StringField)
genres = db.ListField(db.StringField)
directors = db.GenericReferenceField(reverse_delete_rule=db.CASCADE)
`

This is the error:
AttributeError: 'GenericReferenceField' object has no attribute 'document_type'

My understanding is that GenericReferenceField inherits ReferenceField attributes.

Start by reproducing the reported Movie model with GenericReferenceField(reverse_delete_rule=db.CASCADE), then compare GenericReferenceField with ReferenceField to trace where document_type is expected. Done means the reported AttributeError is resolved and the reverse-delete behavior is covered by a regression test; the issue names no specific files or existing tests.