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"

      TYPE_RST_STREAM -> readRstStream(handler, length, flags, streamId)
      TYPE_SETTINGS -> readSettings(handler, length, flags, streamId)
      TYPE_PUSH_PROMISE -> readPushPromise(handler, length, flags, streamId)
      TYPE_PING -> readPing(handler, length, flags, streamId)
      TYPE_GOAWAY -> readGoAway(handler, length, flags, streamId)
      TYPE_WINDOW_UPDATE -> readWindowUpdate(handler, length, flags, streamId)

            return a;
        }
        if (a.length == 0) {
            return b;
        }
        if (b.length == 0) {
            return a;
        }
        final boolean[] array = (boolean[]) Array.newInstance(boolean.class, a.length + b.length);
        System.arraycopy(a, 0, array, 0, a.length);
        System.arraycopy(b, 0, array, a.length, b.length);
        return array;
    }

    /**

   */
  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;
  }