Default value with expression used in BPMN

Is it possible to provide a default value for a property?

I am using a User Task with a Timer boundary event and have provided a timeout value so that the User Task times out.
I have used a property expression ${userTaskTimeout}, and I am providing this value while executing the workflow.

The scenario is that this value will be provided by some other service that will trigger this BPMN process. Right now they have not added this value while starting the process.

Is there any way I can add a default value for this property ${userTaskTimeout} in BPMN, and later when the calling service provides this value then it will be taken from there?

Any way to add a default value with the property as we add in the Spring application.yml file