function exportValue(&$submitValues, $assoc = false) {
        global $USER;

        $draftitemid = $this->_findValue($submitValues);
        if (null === $draftitemid) {
            $draftitemid = $this->getValue();
        }

        // make sure max one file is present and it is not too big
        if (!is_null($draftitemid)) {
            $fs = get_file_storage();
            $usercontext = context_user::instance($USER->id);
            if ($files = $fs->get_area_files($usercontext->id, 'user', 'draft', $draftitemid, 'id DESC', false)) {
                $file = array_shift($files);
                if ($this->_options['maxbytes']
                    and $this->_options['maxbytes'] !== USER_CAN_IGNORE_FILE_SIZE_LIMITS
                    and $file->get_filesize() > $this->_options['maxbytes']) {

                    // bad luck, somebody tries to sneak in oversized file
                    $file->delete();
                }
                foreach ($files as $file) {
                    // only one file expected
                    $file->delete();
                }
            }
        }

        return $this->_prepareValue($draftitemid, true);
    }