public void appendString(CharSequence val) {
            assert columnTypes[curColIndex] == SQLType.VARCHAR;

            byte[] bytes = UTF8Util.toUtf8(val);
            appendUTF8String(bytes);
        }
A simple row can only store simple values like int, double, string. But cannot store multi-value column.
indexr-segment/src/main/java/io/indexr/segment/helper/SimpleRow.java