code: private ByteBuffer successor(@Nullable ByteBuffer buf) {
          if (buf == null) {
              return ByteBuffer.allocate(0);
          }
          ByteBuffer next = ByteBuffer.allocate(buf.remaining() + 1);
          next.put(buf.duplicate());
          next.put((byte) 0);
          next.flip();
          return next;
      }
docs: Returns a ByteBuffer that, w/unsigned comparison, sorts immediately after the specified {@code buf}.