@Override
                    public void complete() {
                        if (completed) {
                            return;
                        }
                        completed = true;
                        writeComplete(out, id);
                        graphqlSubscriptions.remove(id);
                    }
Receives an event and returns a response if one should be sent.
graphql/src/main/java/com/linecorp/armeria/server/graphql/GraphqlWSSubProtocol.java