docs: public Jar addPackageOf(Class<?> clazz, Filter filter) throws IOException {
          try {
              final String path = clazz.getPackage().getName().replace('.', '/');
              URL dirURL = clazz.getClassLoader().getResource(path);
              if (dirURL != null && dirURL.getProtocol().equals("file"))
                  addDir(Paths.get(path), Paths.get(dirURL.toURI()), filter, false);
              else {
                  if (dirURL == null) // In case of a jar file, we can't actually find a directory.
                      dirURL = clazz.getClassLoader().getResource(clazz.getName().replace('.', '/') + ".class");
  
                  if (dirURL.getProtocol().equals("jar")) {
                      final URI jarUri = new URI(dirURL.getPath().substring(0, dirURL.getPath().indexOf('!')));
                      try (JarInputStream jis1 = newJarInputStream(Files.newInputStream(Paths.get(jarUri)))) {
                          for (JarEntry entry; (entry = jis1.getNextJarEntry()) != null;) {
                              try {
                                  if (entry.getName().startsWith(path + '/')) {
                                      if (filter == null || filter.filter(entry.getName()))
                                          addEntryNoClose(jos, entry.getName(), jis1);
                                  }
                              } catch (ZipException e) {
                                  if (!e.getMessage().startsWith("duplicate entry"))
                                      throw e;
                              }
                          }
                      }
                  } else
                      throw new AssertionError();
              }
              return this;
          } catch (URISyntaxException e) {
              throw new AssertionError(e);
          }
      }