Self referential properties cause infinite recursion

[devraj]

class ProtocolDocumentArea(types.Model):

    protocol_document_area_id = types.Integer()
    standard_edition_id = types.Integer()

    area_name = types.String(max_length=255)
    area_number = types.Integer()

    created_date = types.DateTime()
    last_updated_date = types.DateTime()

#: Defines a self referencial relationship
ProtocolDocumentArea.sub_areas = types.Array(element_template=ProtocolDocumentArea())