code: @SafeVarargs
    public final DataSet row(Object... columnValues) {
      checkIfNotReadOnly();
      if (columnValues.length != source.getColumnCount()) {
        throw new InvalidOperationException(source.getColumnCount() +
            " columns expected, not " + columnValues.length + ".");
      }
      addRow(new Row(columnValues));
      return this;
    }
docs: Add a row to the data set.
  @param columnValues Column values forming a row.
  @return The data set instance (for chained calls).
  @throws InvalidOperationException if this data set is read-only.
  @see #rows(Object[][])
  @see #add(DataSet)
  @see #isReadOnly()