I attach the influence diagram of the "decision test problem" to reproduce the issue.
If the user imposes a policy in the GUI on the decision "Do test?", executes the inference (button "Edition/Inference mode"), and then right clicks on "Show optimal policy" over "Do test?" then there is a NullPointerException in the GUI.
One possible solution for this issue would be to disable the options "Show optimal policy" and "Show expected utilities" in those decision nodes with policies imposed.