code: protected final void putMessage(Http2Stream stream, FullHttpMessage message) {
          FullHttpMessage previous = stream.setProperty(messageKey, message);
          if (previous != message && previous != null) {
              previous.release();
          }
      }
docs: Make {@code message} be the state associated with {@code stream}.
  @param stream The stream which {@code message} is associated with.
  @param message The message which contains the HTTP semantics.