code: public static void pack(File rootDir, File zip, int compressionLevel) {
      pack(rootDir, zip, IdentityNameMapper.INSTANCE, compressionLevel);
    }
docs: Compresses the given directory and all its sub-directories into a ZIP file.
  <p>
  The ZIP file must not be a directory and its parent directory must exist.
  Will not include the root directory name in the archive.
  
  @param rootDir
  root directory.
  @param zip
  ZIP file that will be created or overwritten.
  @param compressionLevel
  compression level