Write to stream fails when "userProperties" is an empy object

[br0wn]

While using protocol version 5, calling writeToStream with userProperties being empty object {} method fails with false as return value. This is the packet being written:

{
  cmd: "publish",
  topic: "protocol-version-debug",
  payload: "{\"pattern\":\"protocol-version-debug\",\"data\":\"{\\\"ok\\\":1724704578895}\"}",
  qos: 0,
  retain: true,
  messageId: 0,
  dup: false,
  properties: {
    userProperties: {
    },
  },
}

I traced the problem to getProperties method which returns false when userProperties is empty object {} because getLengthProperty for empty object returns 0 causing getProperties to return false:

https://github.com/mqttjs/mqtt-packet/blob/1f2cf7f98ae036fae97096299d6237ae442ff9d8/writeToStream.js#L1004

Setting userProperties to something like {'f': 'u'} removes the issue.

We are using ClientMqtt from @nestjs/microservices to emit data to a topic.

const {
	MqttRecordBuilder,
	ClientProxyFactory,
	Transport
} = require('@nestjs/microservices');

const client = ClientProxyFactory.create({
	transport: Transport.MQTT,
	options: {
		url: 'mqtt://0.0.0.0:1883',	
		protocolVersion: 5,	
	}
})

const record = new MqttRecordBuilder()
	.setData(JSON.stringify({ ok: new Date().getTime() }))
	.setRetain(true)
	.build();

client.emit('protocol-version-debug', record);

It seems the ClientMqtt sets userProperties to empty object when no userProperties is provided:

https://github.com/nestjs/nest/blob/e4b07eb06b406183e708269e0439f442a1dadb1c/packages/microservices/client/client-mqtt.ts#L217

[mcollina]

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