ExtensibleXmlParser error : The content of element 'bpmn2:ioSpecification' is not complete. One of ... is expected

Issue

• While deploying an application (say, EAR) which packages a kjar consisting of a BPMN2 process definition, it throws the following error. Interestingly, the process definition just contains couple of User Task nodes apart from a Start and End node.

ERROR [org.drools.core.xml.ExtensibleXmlParser] (MSC service thread 1-20 (null:47, 31): cvc-complex-type.2.4.b:  the content of element 'bpmn2:ioSpecification' is not complete.  One of '{"http://omg.org/spec/BPMN/20100524/MODEL":inputSet, "http://www.omg.org/spec/BPMN/20100524/MODEL":outputSet}' is expected.
INFO [org.drools,compiler.kie.builder.impl.KieRepositoryImpl] (MSC service thread 1-2) KieModule was added:ZipKieModule[ ReleaseId=org.sample.models:KieProject:1.0file=/home/test/.m2/repostory/org/sample/models/KieProject/1.0/KieProject-1.0.jar]
...

How to fix this issue and figure out what's wrong with the process definition?
- I get the following error when I start a Container

2018-01-12 21:20:05,512 ERROR [org.drools.core.xml.ExtensibleXmlParser][690] (EJB default - 1) Process Info: id:com.sample.MyProcess, pkg:com.sample, name:MyProcess, version:1.0
Node Info: id: name:
Parser message: (null: 35, 31): 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":inputSet, "http://www.omg.org/spec/BPMN/20100524/MODEL":outputSet}' is expected.

A userTask of the process is:

    <bpmn2:userTask id="_4D8F330C-E327-4B6F-A3CA-AD3220554CAA" drools:selectable="true" drools:scriptFormat="http://www.java.com/java" color:background-color="#fafad2" color:border-color="#000000" color:color="#000000" name="MyTask">
      <bpmn2:extensionElements>
        <drools:metaData name="elementname">
          <drools:metaValue><![CDATA[MyTask]]></drools:metaValue>
        </drools:metaData>
      </bpmn2:extensionElements>
      <bpmn2:incoming>_62A0EF34-F93A-4C19-93DE-3F8E96395ACF</bpmn2:incoming>
      <bpmn2:outgoing>_23E4EA8B-56A4-4FAC-A775-6BCC63D0489C</bpmn2:outgoing>
      <bpmn2:ioSpecification id="_8cO10WtqEeeE9cemtijsUw">
        <bpmn2:dataInput id="_4D8F330C-E327-4B6F-A3CA-AD3220554CAA_SkippableInputX" name="Skippable"/>
        <bpmn2:inputSet id="_8cO10mtqEeeE9cemtijsUw">
          <bpmn2:dataInputRefs>_4D8F330C-E327-4B6F-A3CA-AD3220554CAA_SkippableInputX</bpmn2:dataInputRefs>
        </bpmn2:inputSet>
      </bpmn2:ioSpecification>