DMMN modeler causes NPE

Flowable Designer
1

When doing a design, whenever there’s an element outside or on the edge of the Case, I get a NPE whenever I try to export the model to XML.

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In this case, the exit sentry is in the edge of a case, and I get NPE:

2019-03-18 15:12:38.826 ERROR 17812 --- [nio-8088-exec-2] o.f.u.m.s.CmmnDisplayJsonConverter       : Error transforming json to pojo 696b0207-44c4-11e9-aabe-186024898a38

java.lang.NullPointerException: null
        at org.flowable.cmmn.editor.json.converter.AssociationJsonConverter.convertJsonToElement(AssociationJsonConverter.java:141) ~[flowable-cmmn-json-converter-6.4.1.jar:6.4.1]
        at org.flowable.cmmn.editor.json.converter.CmmnJsonConverter.convertToCmmnModel(CmmnJsonConverter.java:354) ~[flowable-cmmn-json-converter-6.4.1.jar:6.4.1]
        at org.flowable.cmmn.editor.json.converter.CmmnJsonConverter.convertToCmmnModel(CmmnJsonConverter.java:288) ~[flowable-cmmn-json-converter-6.4.1.jar:6.4.1]
        at org.flowable.ui.modeler.service.CmmnDisplayJsonConverter.processCaseElements(CmmnDisplayJsonConverter.java:60) [flowable-ui-modeler-logic-6.4.1.jar:6.4.1]
        at org.flowable.ui.modeler.rest.app.EditorDisplayJsonClientResource.getModelJSON(EditorDisplayJsonClientResource.java:52) [flowable-ui-modeler-rest-6.4.1.jar:6.4.1]
        at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:?]
        at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:?]
        at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:?]

I think I added the main part of the stack-trace which is very long, the rest is Spring/Tomcat servlet and security stuff. Let me know if you want to see more