code: public final String getString(int columnIndex) {
          validateColumnType(columnIndex, VoltType.STRING);
          String retval = readString(getOffset(columnIndex), VoltTable.ROWDATA_ENCODING);
          m_wasNull = (retval == null);
          return retval;
      }
docs: Retrieve the {@link java.lang.String String} value stored in the column specified by index.
  Looking at the return value is not a reliable way to check if the value
  is <tt>null</tt>. Use {@link #wasNull()} instead. If at all possible you should use {@link #getStringAsBytes(int)} instead
  and avoid the overhead of constructing the {@link java.lang.String String} object.
  @param columnIndex Index of the column
  @return {@link java.lang.String String} value stored in the specified column
  @see #wasNull()