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;
  }

      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

    checkNotNull(array);
    checkPositionIndexes(fromIndex, toIndex, array.length);
    if (array.length <= 1) {
      return;
    }

    int length = toIndex - fromIndex;
    // Obtain m = (-distance mod length), a non-negative value less than "length". This is how many
    // places left to rotate.
    int m = -distance % length;
    m = (m < 0) ? m + length : m;

      offset = min(offset, this.length);
      length = min(length, this.length - offset);
      int newOffset = this.offset + (int) offset;
      return new ByteArrayByteSource(bytes, newOffset, (int) length);
    }

    @Override
    public String toString() {
      return "ByteSource.wrap("

    }

    @Override
    public K[] createKeyArray(int length) {
      return ((TestMultimapGenerator<K, V, M>) multimapGenerator.getInnerGenerator())
          .createKeyArray(length);
    }

    @SuppressWarnings("unchecked")
    @Override
    public Collection<V>[] createValueArray(int length) {
      return (Collection<V>[]) new Collection<?>[length];
    }
  }

    @Override
    public InputStream openStream() {
      return new In();
    }

    public void append(byte[] b) {
      byte[] newBytes = Arrays.copyOf(bytes, bytes.length + b.length);
      System.arraycopy(b, 0, newBytes, bytes.length, b.length);
      bytes = newBytes;
    }

    private class In extends InputStream {
      private int pos;

      @Override
      public int read() throws IOException {

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