Python PonyORM One to one mapping

I am trying to create a one-to-one mapping using Pony ORM.

class ApplierIngress(ApplierObjectMapper.db.Entity):
    correlation_id = orm.PrimaryKey(str)
    ticket_number  = orm.Required(str)
    username       = orm.Required(str)
    status         = orm.Required(str)
    request_date   = orm.Required(datetime)

class ApplierResult(ApplierObjectMapper.db.Entity):
    correlation_id = orm.Required(ApplierIngress)
    result         = orm.Required(orm.LongStr)
    request_date   = orm.Required(datetime)

It throws error while generating the mapping

pony.orm.core.ERDiagramError: Reverse attribute for ApplierResult.correlation_id not found

I want correlation_id in ApplierResult table be the foreign key referencing to correlation_id in ApplierIngress table

Please let me know what am I doing wrong?