code: @Nonnull
    public CompletableFuture<Optional<Object>> send(final Object data) {
      return event(data).send();
    }
docs: Send an event.
  
  <pre>{@code
  sse.send(new MyObject());
  }</pre>
  
  <pre>{@code
  sse.send(new MyObject(), "json").whenComplete((id, x) -> {
  if (x == null) {
  handleSuccess();
  } else {
  handleError(x);
  }
  });
  }</pre>
  
  The <code>id</code> of the success callback correspond to the {@link Event#id()}.
  
  @param data Event data.
  @return A future. The success callback contains the {@link Event#id()}.