static public function isQtiFile(Variable $variable, $considerNull = true) {
        
        $correctBaseType = $variable->getBaseType() === BaseType::FILE;
        $correctCardinality = $variable->getCardinality() === Cardinality::SINGLE;
        $nullConsideration = ($considerNull === true) ? true : $variable->getValue() !== null;
        
        return $correctBaseType === true && $correctCardinality === true && $nullConsideration === true;
    }