Thanks Sandra!
It really looks better. I get no exceptions and I am able to create a BPMN diagram. I only want to add information that that plugin can be found here:
https://repository.jboss.org/nexus/content/groups/public-jboss/org/drools/org.drools.updatesite/5.5.0.Beta1/org.drools.updatesite-5.5.0.Beta1-assembly.zip
kr,
Tadeusz