code: public final byte[] getStringAsBytes(int columnIndex) {
          validateColumnType(columnIndex, VoltType.STRING);
          int pos = m_buffer.position();
          m_buffer.position(getOffset(columnIndex));
          int len = m_buffer.getInt();
          if (len == VoltTable.NULL_STRING_INDICATOR) {
              m_wasNull = true;
              m_buffer.position(pos);
              return null;
          }
          m_wasNull = false;
          byte[] data = new byte[len];
          m_buffer.get(data);
          m_buffer.position(pos);
          return data;
      }
docs: Retrieve the <tt>string</tt> value stored in the column specified by index as
  an array of bytes. Assume UTF-8 encoding for all string values in VoltDB.
  Looking at the return value is not a reliable way to check if the value
  is <tt>null</tt>. Use {@link #wasNull()} instead.
  @param columnIndex Index of the column
  @return <tt>string</tt> value stored in the specified column as a <tt>byte[]</tt>
  @see #wasNull()