code: public File getUserOutputFile(String relativePath) {
          if (relativePath == null)
              return outputRoot;
          else
              return new File(outputRoot, relativePath);
      }
docs: Allocate a file in the user output directory, e.g.
  WLP_OUTPUT_DIR/relativePath
  
  @param relativePath
  relative path of file to create in the WLP_OUTPUT_DIR directory
  @return File object for relative path, or for the WLP_OUTPUT_DIR directory itself
  if the relative path argument is null