docs: void setRightChild(final byte b, @NotNull final MutableNode child) {
          final ChildReference right = children.getRight();
          if (right == null || (right.firstByte & 0xff) != (b & 0xff)) {
              throw new IllegalArgumentException();
          }
          children.setAt(children.size() - 1, new ChildReferenceMutable(b, child));
      }