static public function isQtiFilePlaceHolder(Variable $variable) {
        
        $correctBaseType = $variable->getBaseType() === BaseType::FILE;
        $correctCardinality = $variable->getCardinality() === Cardinality::SINGLE;
        
        if ($correctBaseType === true && $correctCardinality === true) {
            
            $value = $variable->getValue();
            $notNull = $value !== null;
            $mime = taoQtiCommon_helpers_PciJsonMarshaller::FILE_PLACEHOLDER_MIMETYPE;
            
            if ($notNull === true && $value->getMimeType() === $mime) {
                return true;
            }
        }
        
        return false;
    }