@Override
    public Writer addRecordEntry(final String columnName, final Object value) {
        if (rowMap == null) {
            rowMap = new HashMap<String, Object>();
        }

        if (!validateColumnTitle(columnName)) {
            throw new IllegalArgumentException("unknown column: \"" + columnName + "\"");
        }
        rowMap.put(columnName, value);
        return this;
    }