WorkflowRuntimeException at inclusiveGatway with default sequenceFlow

I designed a bpmn process with an inclusive gateway with 3 outgoing sequence flows. the first and the second with a condition and the third as default. The bpmn file is attached. Wenn I try to start the process with the variable 'test' set to "c" for not matching the conditions of the first and second sequence flow I get the following Exception in the server.log

WARN [org.drools.persistence.SingleSessionCommandService] (http-localhost-127.0.0.1-8080-4) Could not commit session: org.jbpm.workflow.instance.WorkflowRuntimeException: [InclusiveGatewayWithDefault:4 - ?:7] – null
at org.jbpm.workflow.instance.node.SplitInstance.internalTrigger(SplitInstance.java:67) [jbpm-flow-6.0.1.Final.jar:6.0.1.Final]
[...]
Caused by: java.lang.NullPointerException
at org.jbpm.workflow.instance.node.SplitInstance.executeStrategy(SplitInstance.java:165) [jbpm-flow-6.0.1.Final.jar:6.0.1.Final]
at org.jbpm.workflow.instance.node.SplitInstance.internalTrigger(SplitInstance.java:63) [jbpm-flow-6.0.1.Final.jar:6.0.1.Final]
... 78 more

If I start the process with fullfilling one or both conditions the process is executed successfully. The same test szenario with an exclusive gateway works.