public function notAllowedIfTrue($attribute, $params)
{
$dependency = $params['dependency'];
$side = $params['side'];
$checker = 'has' . ucfirst($side);
if ($this->{$checker}() && $this->{$dependency} && $this->{$attribute}) {
$this->addError($attribute, ucfirst($side) . ' ' . $this->getAttributeLabel($attribute) . ' cannot be set when ' . $side . ' ' . $this->getAttributeLabel($dependency) . ' is set');
}
}