code: private void validateSchema(Schema schema) throws DDFException {
      Set<String> columnSet = new HashSet<String>();
      if(schema != null && schema.getColumns() != null) {
        for (Column column : schema.getColumns()) {
          if (columnSet.contains(column.getName())) {
            throw new DDFException(String.format("Duplicated column name %s", column.getName()));
          } else {
            columnSet.add(column.getName());
          }
        }
      }
    }
docs: ////// MetaData that deserves to be right here at the top level ////////