The message that the server should publish in the event of an ungraceful disconnection.
The WillMessage will only be sent to the server when Connect is called if WillTopic is set. Note that in MQTTSN the clean session concept is extended to will topic and will message. The WillMessage can be updated with the UpdateWillMessage method.
Refer to WillTopic for more information about MQTT Will functionality.
This property is not available at design time.