Entity conditions don't work in storyboard stop trigger

When trying to use an EntityCondition in the StopTrigger of a Storyboard, we get this exception:

C++ exception with description "Requested key [EntityBroker] is not accessible in blackboard." thrown in the test body.

The problem is that the EntityBroker is only registered in ManeuverGroups in the blackboard, so triggering entities of the EntityCondition can be used as actors in the actions of the Maneuver. In the StopTrigger of the Storyboard this use-case is not applicable because there is no enclosing ManeuverGroup, so the EntityBroker is not set in the blackboard in this case.

The proposal would be to adjust the generator and EntityConditions in a way that the EntityBroker is used only if it was set. A first example is implemented here