/** * Checks if a property value is null. * This method overrides the parent implementation by checking * if the key exists in the collection and contains a non-null value. * @param string $name the property name or the event name * @return boolean whether the property value is null */ public function __isset($name) { if ($this->contains($name)) { return $this->itemAt($name) !== null; } else { return parent::__isset($name); } }