How do you simulate a ReadStructuralFeature action in an activity diagram?

[mse]

The documentaiton (see https://sparxsystems.com/enterprise_architect_user_guide/14.0/model_domains/actionnotation.html) for model simulation does not go into details on how to simulate a read structural feature action. I tried it with an atomic action and I can simulate the data and control flows fine. However when I switch to ReadStructuralFeature action, the simulation stops at that action and does not progress.

How do you properly model and simulate the reading of a value from a port using the ReadStructuralFeature action?

[mse]

Basically, the documentationi states the following:

Resembles AddStructuralFeatureValue, except that the value Port is not necessary.

In a simulation, if the Object's Port has no value at run time, the simulation will pause at the Action.

What does it mean for the "object's port" to have a value?