public function containsNull()
    {
        foreach (array_keys($this->getDataPlaceHolder()) as $key) {
            $v = $this[$key];
            if ($v instanceof Container && $v->isNull()) {
                return true;
            } elseif (($v instanceof QtiString && $v->getValue() === '') || is_null($v)) {
                return true;
            }
        }

        return false;
    }
public function containsNull()
    {
        foreach (array_keys($this->getDataPlaceHolder()) as $key) {
            $v = $this[$key];
            if ($v instanceof Container && $v->isNull()) {
                return true;
            } elseif (($v instanceof QtiString && $v->getValue() === '') || is_null($v)) {
                return true;
            }
        }

        return false;
    }
public function containsNull ( ) { foreach ( array_keys ( $ this -> getDataPlaceHolder ( ) ) as $ key ) { $ v = $ this [ $ key ] ; if ( $ v instanceof Container && $ v -> isNull ( ) ) { return true ; } elseif ( ( $ v instanceof QtiString && $ v -> getValue ( ) === '' ) || is_null ( $ v ) ) { return true ; } } return false ; }
Wether the collection contains a QTI Runtime compliant value which is
considered to be NULL.

* If the collection of operands is empty, true is returned.
* If the collection of operands contains null, an empty container, or an empty string, true is returned.
* In any other case, false is returned.

@return boolean
Wether the collection contains a QTI Runtime compliant value which is considered to be NULL .