Error logged if we use reusable subprocess node with no dataOutput mapping in stunner designer.

Issue

• Error logged if we use reusable subprocess node with no dataOutput mapping in stunner designer.

ERROR [org.drools.core.xml.ExtensibleXmlParser] (default task-9) Process Info: id:ReusableProcessNodeTest.Process1, pkg:org.jbpm, name:Process1, version:1.0 
Node Info: id:_8GmcIN5vEemqXdhtZWYSEQ name: 
Parser message: (null: 35, 60): cvc-complex-type.2.4.b: The content of element 'bpmn2:ioSpecification' is not complete. One of '{"http://www.omg.org/spec/BPMN/20100524/MODEL":documentation, "http://www.omg.org/spec/BPMN/20100524/MODEL":extensionElements, "http://www.omg.org/spec/BPMN/20100524/MODEL":dataInput, "http://www.omg.org/spec/BPMN/20100524/MODEL":dataOutput, "http://www.omg.org/spec/BPMN/20100524/MODEL":inputSet}' is expected.