private static void writeNext(WebSocketWriter out, String operationId, ExecutionResult executionResult)
            throws JsonProcessingException {
        final Map<String, Object> response = ImmutableMap.of(
                "id", operationId,
                "type", "next",
                "payload", executionResult.toSpecification());
        final String event = serializeToJson(response);
        logger.trace("NEXT: {}", event);
        out.tryWrite(event);
    }
This only works reliably if maybeMap is from Json, as maps(objects) in Json
can only have string keys.
graphql/src/main/java/com/linecorp/armeria/server/graphql/GraphqlWSSubProtocol.java