code: public List<InputColumn<?>> getOutputColumns() {
          final List<InputColumn<?>> result = new ArrayList<>();
          for (final RowProcessingConsumer consumer : _consumers) {
              final InputColumn<?>[] outputColumns = consumer.getOutputColumns();
              for (final InputColumn<?> outputColumn : outputColumns) {
                  result.add(outputColumn);
              }
          }
          return result;
      }
docs: Gets the output columns produced by all the consumers of this
  {@link ConsumeRowHandler}.
  
  @return