public function getId()
    {
        $value = $this->getFirstValue(PropertyIds::OBJECT_ID);
        if (is_string($value)) {
            return $value;
        }
        return null;
    }
public function getId()
    {
        $value = $this->getFirstValue(PropertyIds::OBJECT_ID);
        if (is_string($value)) {
            return $value;
        }
        return null;
    }
public function getId ( ) { $ value = $ this -> getFirstValue ( PropertyIds :: OBJECT_ID ) ; if ( is_string ( $ value ) ) { return $ value ; } return null ; }
Returns the object ID.

@return string|null the object ID or <code>null</code> if the object ID is unknown
Returns the object ID .