docs: public boolean isSigned(int column) throws SQLException
      {
          sourceResultSet.checkColumnBounds(column);
          VoltType type = sourceResultSet.table.getColumnType(column - 1);
          Boolean result = type.isUnsigned();
          if (result == null) {
              // Null return value means 'not signed' as far as this interface goes
              return false;
          }
          return !result;
      }