if lang is None:
        return None
    lang = lang.lower()
    return lang


def complete_existing_lang(incomplete: str):
    lang_path: Path
    for lang_path in get_lang_paths():
        if lang_path.is_dir() and lang_path.name.startswith(incomplete):
            yield lang_path.name


@app.callback()
def callback() -> None:
    if is_mkdocs_insiders():
        os.environ["INSIDERS_FILE"] = "../en/mkdocs.insiders.yml"

   */
  static @Nullable Object[] copyAsObjectArray(@Nullable Object[] elements, int offset, int length) {
    checkPositionIndexes(offset, offset + length, elements.length);
    if (length == 0) {
      return new Object[0];
    }
    @Nullable Object[] result = new Object[length];
    arraycopy(elements, offset, result, 0, length);
    return result;
  }

  @CanIgnoreReturnValue

   */
  public static boolean[] concat(boolean[]... arrays) {
    long length = 0;
    for (boolean[] array : arrays) {
      length += array.length;
    }
    boolean[] result = new boolean[checkNoOverflow(length)];
    int pos = 0;
    for (boolean[] array : arrays) {
      System.arraycopy(array, 0, result, pos, array.length);
      pos += array.length;
    }
    return result;
  }

   */
  public static boolean[] concat(boolean[]... arrays) {
    long length = 0;
    for (boolean[] array : arrays) {
      length += array.length;
    }
    boolean[] result = new boolean[checkNoOverflow(length)];
    int pos = 0;
    for (boolean[] array : arrays) {
      System.arraycopy(array, 0, result, pos, array.length);
      pos += array.length;
    }
    return result;
  }

        assertEquals(2, protocolHelper.getWebProtocols().length);
        assertEquals(3, protocolHelper.getFileProtocols().length);
    }

    public void test_loadProtocols() {
        final ProtocolHelper protocolHelper = new ProtocolHelper();
        protocolHelper.loadProtocols("org.codelibs.fess.test.net.protocol");

        assertEquals(1, protocolHelper.getWebProtocols().length);

   */
  public static short[] concat(short[]... arrays) {
    long length = 0;
    for (short[] array : arrays) {
      length += array.length;
    }
    short[] result = new short[checkNoOverflow(length)];
    int pos = 0;
    for (short[] array : arrays) {
      System.arraycopy(array, 0, result, pos, array.length);
      pos += array.length;
    }
    return result;
  }

   */
  public static short[] concat(short[]... arrays) {
    long length = 0;
    for (short[] array : arrays) {
      length += array.length;
    }
    short[] result = new short[checkNoOverflow(length)];
    int pos = 0;
    for (short[] array : arrays) {
      System.arraycopy(array, 0, result, pos, array.length);
      pos += array.length;
    }
    return result;
  }

   */
  public static char[] concat(char[]... arrays) {
    long length = 0;
    for (char[] array : arrays) {
      length += array.length;
    }
    char[] result = new char[checkNoOverflow(length)];
    int pos = 0;
    for (char[] array : arrays) {
      System.arraycopy(array, 0, result, pos, array.length);
      pos += array.length;
    }
    return result;
  }

      String[] suffix = {"f", "g"};
      String[] all = new String[elements.length + suffix.length];
      arraycopy(elements, 0, all, 0, elements.length);
      arraycopy(suffix, 0, all, elements.length, suffix.length);
      return ImmutableList.copyOf(all).subList(0, elements.length);
    }
  }

  public static class ImmutableListTailSubListGenerator extends TestStringListGenerator {
    @Override

    }

    if (slice && bytes.length > 0) {
      // test a random slice() of the ByteSource
      Random random = new Random();
      byte[] expected = factory.getExpected(bytes);
      // if expected.length == 0, off has to be 0 but length doesn't matter--result will be empty
      int off = expected.length == 0 ? 0 : random.nextInt(expected.length);
      int len = expected.length == 0 ? 4 : random.nextInt(expected.length - off);