Model API cannot set values to null

[ThorbenLindhauer]

This issue was imported from JIRA:

Field	Value
JIRA Link	CAM-4178
Reporter	rP62zaw What is this name? This pseudonym name was generated based on the user name in JIRA to protect the personal data of our JIRA users. You can use this identifier to search for issues by the same reporter.
Has restricted visibility comments	false

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See the test case below. It fails with this exception:

org.camunda.bpm.engine.ProcessEngineException: Delegate expression  did neither resolve to an implementation of interface org.camunda.bpm.engine.impl.pvm.delegate.ActivityBehavior nor interface org.camunda.bpm.engine.delegate.JavaDelegate
    at org.camunda.bpm.engine.impl.bpmn.behavior.ServiceTaskDelegateExpressionActivityBehavi

As you can see a "ServiceTaskDelegateExpressionActivityBehavior" was choosen - even if I set

    serviceTask.setCamundaDelegateExpression(null);

I digged a bit into it and found that this results in havind the

   delegateExpression=""

Hence an empty string instead of null.

Not sure if this is a bug in the ModelAPI or if it should better be checked for emptry string in https://github.com/camunda/camunda-bpm-platform/blob/master/engine/src/main/java/org/camunda/bpm/engine/impl/bpmn/parser/BpmnParse.java#L1697 as done with expressions as well. https://github.com/camunda/camunda-bpm-platform/blob/master/engine/src/main/java/org/camunda/bpm/engine/impl/bpmn/parser/BpmnParse.java#L1703

 @Test
  public void testModelApiBug() {
    BpmnModelInstance modelInstance = Bpmn.createEmptyModel();
    Definitions definitions = modelInstance.newInstance(Definitions.class);
    definitions.setTargetNamespace("http://camunda.org/examples");
    modelInstance.setDefinitions(definitions);
    org.camunda.bpm.model.bpmn.instance.Process process = modelInstance.newInstance(org.camunda.bpm.model.bpmn.instance.Process.class);
    process.setId("test");
    definitions.addChildElement(process);

    StartEvent startEvent = modelInstance.newInstance(StartEvent.class);
    startEvent.setAttributeValue("id", "startEvent1", true);   
    process.addChildElement(startEvent);

    ServiceTask serviceTask = modelInstance.newInstance(ServiceTask.class);
    serviceTask.setAttributeValue("id", "serviceTask1", true);   
    serviceTask.setCamundaClass(null);
    serviceTask.setCamundaDelegateExpression(null);
    serviceTask.setCamundaExpression("#{true}"); // Noop
    process.addChildElement(serviceTask);

    createSequenceFlow(process, startEvent, serviceTask);

    repositoryService().createDeployment().addModelInstance("test.bpmn", modelInstance).deploy();
    runtimeService().startProcessInstanceByKey("test");
  }

  public SequenceFlow createSequenceFlow(org.camunda.bpm.model.bpmn.instance.Process process, FlowNode from, FlowNode to) {
    String identifier = from.getId() <ins> "-" </ins> to.getId();
    SequenceFlow sequenceFlow = createElement(process, identifier, SequenceFlow.class);
    process.addChildElement(sequenceFlow);
    sequenceFlow.setSource(from);
    from.getOutgoing().add(sequenceFlow);
    sequenceFlow.setTarget(to);
    to.getIncoming().add(sequenceFlow);
    return sequenceFlow;
  }
  protected <T extends BpmnModelElementInstance> T createElement(BpmnModelElementInstance parentElement, String id, Class<T> elementClass) {
    T element = parentElement.getModelInstance().newInstance(elementClass);
    element.setAttributeValue("id", id, true);
    parentElement.addChildElement(element);
    return element;
  }

Links:

[ThorbenLindhauer]

This comment was imported from JIRA and written by user zZ6Eda

What is this name?

This pseudonym name was generated based on the user name in JIRA to protect the personal data of our JIRA users. You can use this identifier to search for issues by the same reporter.

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Is this a valid workaround?

serviceTask.removeAttributeNs(org.camunda.bpm.model.bpmn.impl.BpmnModelConstants.CAMUNDA_NS, "delegateExpression")

[ThorbenLindhauer]

This comment was imported from JIRA and written by user @nevries

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This clearly also happens on

UserTask.setCamundaAssignee(null);
UserTask.setCamundaCandidateGroups(null);
...

Hence, setting assignee to null yields in a user task that is always assigned to a user with name empty string. Unpleasent behaviour...