code: public URI getInputMap() {
  //       return toURI(getProperty(INPUT_DITAMAP_URI));
          return files.values().stream()
                  .filter(fi -> fi.isInput)
                  .map(fi -> getInputDir().relativize(fi.src))
                  .findAny()
                  .orElse(null);
      }
docs: Get input file
  
  @return input file path relative to input directory, {@code null} if not set