code: @Override
      public AbstractPipelineOutput execute(final AbstractPipelineInput input)
              throws DITAOTException {
          final Collection<FileInfo> fis = job.getFileInfo(fileInfoFilter);
          for (final FileInfo f: fis) {
              final URI file = job.tempDirURI.resolve(f.uri);
              logger.info("Processing " + file);
              try {
                  xmlUtils.transform(file, getProcessingPipe(f));
              } catch (final DITAOTException e) {
                  logger.error("Failed to process XML filter: " + e.getMessage(), e);
              }
          }
          return null;
      }
docs: Filter files through XML filters.
  
  @param input Input parameters and resources.
  @return always returns {@code null}