copy method
Returns a copy of this
EntityReference instance.
Implementation
@override
EntityReference<T> copy({bool withEntity = true}) {
var cp = EntityReference<T>._(
_type,
_typeName,
_id,
withEntity ? _entity : null,
null,
_entityHandler,
_entityProvider,
_entityHandlerProvider,
_entityFetcher,
_entityCache,
false);
if (withEntity) cp._entityTime = _entityTime;
return cp;
}