code: private List<File> asFiles(File srcDir, String[] files, FileNameMapper m) {
      List<File> newFiles = new ArrayList<>();
      for(String file : files) {
        boolean hasMatchingExtension = m.mapFileName(file) != null; //use mapFileName as a check to validate if the source file extension is recognized by the mapper or not
        if(hasMatchingExtension) {
          newFiles.add(new File(srcDir, file));
        }
      }
      return newFiles;
    }
docs: Converts an array of relative String filenames to a {@code List<File>}
  @param srcDir The root directory of all files
  @param files All files are relative to srcDir
  @return a List of Files by joining srcDir to each file