protected function readHeaderRow($rowNumber)
    {
        $this->file->seek($rowNumber);
        $headers = $this->file->current();

        // Test for duplicate column headers
        $diff = array_diff_assoc($headers, array_unique($headers));
        if (count($diff) > 0) {
            switch ($this->duplicateHeadersFlag) {
                case self::DUPLICATE_HEADERS_INCREMENT:
                    $headers = $this->incrementHeaders($headers);
                    // Fall through
                case self::DUPLICATE_HEADERS_MERGE:
                    break;
                default:
                    throw new DuplicateHeadersException($diff);
            }
        }

        return $headers;
    }