fix(drilldown): ignore elements without BusinessObject

lib/features/drilldown/SubprocessCompatibility.js

@@ -68,6 +68,11 @@ SubprocessCompatibility.prototype.createNewDiagrams = function(plane) {
 
   plane.get('planeElement').forEach(function(diElement) {
     var bo = diElement.bpmnElement;
+
+    if (!bo) {
+      return;
+    }
+
     var parent = bo.$parent;
 
     if (is(bo, 'bpmn:SubProcess') && !diElement.isExpanded) {

test/spec/features/drilldown/legacy-subprocesses.bpmn

@@ -50,6 +50,9 @@
       <bpmndi:BPMNShape id="Activity_1hpaeri_di" bpmnElement="emptyProcess">
         <dc:Bounds x="960" y="50" width="100" height="80" />
       </bpmndi:BPMNShape>
+      <bpmndi:BPMNShape id="ignored_di">
+        <dc:Bounds x="0" y="0" width="100" height="80" />
+      </bpmndi:BPMNShape>
     </bpmndi:BPMNPlane>
   </bpmndi:BPMNDiagram>
 </bpmn:definitions>