/**
* 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);
}
}
