@Override protected V doExecute() throws IOException {
    // TODO: testme
    for (EventExecutor eventLoop : httpClient.options().factory().eventLoopGroup()) {
      if (eventLoop.inEventLoop()) {
        throw new RuntimeException("""
          Attempting to make a blocking request from an event loop. \
          Either use doEnqueue() or run this in a separate thread.\
          """);
      }
    }
    final AggregatedHttpResponse response;
    try {
      response = sendRequest().join();
    } catch (CompletionException e) {
      propagateIfFatal(e);
      Exceptions.throwUnsafely(e.getCause());
      return null;  // Unreachable
    }
    return parseResponse(response, bodyConverter);
  }
Returns the {@linkplain HttpHeaders headers} for this request.
zipkin-storage/elasticsearch/src/main/java/zipkin2/elasticsearch/internal/client/HttpCall.java