public function containsNullOnly()
    {
        $data = $this->getDataPlaceHolder();
        
        foreach ($data as $variable) {
            $value = $variable->getValue();
            
            if ($variable->isNull() === false) {
                return false;
            }
        }
        
        return true;
    }
public function containsNullOnly()
    {
        $data = $this->getDataPlaceHolder();
        
        foreach ($data as $variable) {
            $value = $variable->getValue();
            
            if ($variable->isNull() === false) {
                return false;
            }
        }
        
        return true;
    }
public function containsNullOnly ( ) { $ data = $ this -> getDataPlaceHolder ( ) ; foreach ( $ data as $ variable ) { $ value = $ variable -> getValue ( ) ; if ( $ variable -> isNull ( ) === false ) { return false ; } } return true ; }
Whether or not the State contains NULL only values.

Please note that in QTI terms, empty containers and empty strings are considered
to be NULL as well. Moreover, if the State is empty of any variable, the method
will return true.

@return boolean
Whether or not the State contains NULL only values .