User::getModelForReferenceField

static function getModelForReferenceField($userId, User $currentFieldValue = null)
{
	if($userId === null)
	{
		return EmptyUser::create();
	}
	if(SystemUser::isSystemUserId($userId))
	{
		return SystemUser::create();
	}
	if(isset($currentFieldValue) && $userId == $currentFieldValue->getId())
	{
		return $currentFieldValue;
	}

	$user = User::loadById($userId);
	if(!$user)
	{
		return EmptyUser::create();
	}

	return $user;
}