Hello,

I believe there is an issue with a Communicator.EventHandler.receivedMessage(Object input) when it tries to logger.trace("Receive a message: {}", message) for a JSON message.

        public void receivedMessage(Object input) {
            Message message = parse(input);
            if (message != null) {
                Object payload = message.getPayload();
                if (payload instanceof Document) {
                    logger.trace("Receive a message: {}", SugarUtil.docToString((Document) payload));
                } else {
                    logger.trace("Receive a message: {}", message);
                }
            }
            if (message instanceof CallResultMessage) {
                events.onCallResult(message.getId(), message.getAction(), message.getPayload());
            } else if (message instanceof CallErrorMessage) {
                failedFlag = true;
                CallErrorMessage call = (CallErrorMessage) message;
                events.onError(call.getId(), call.getErrorCode(), call.getErrorDescription(), call.getRawPayload());
            } else if (message instanceof CallMessage) {
                CallMessage call = (CallMessage) message;
                events.onCall(call.getId(), call.getAction(), call.getPayload());
            }
        }

What I`m getting in a log console is:

FINEST [03:19:20 23-Jan-19 PST][eu.chargetime.ocpp.Communicator] Receive a message: eu.chargetime.ocpp.model.CallMessage@9023eb

While in a Wireshark I can see:

[2, "69015629", "Heartbeat", {}]

Could it be something to do with a missing .toString() method for a Message class?