fix(util): fix isExpanded check

DiUtil/isExpanded now returns either true or false instead of
'undefined' in some cases.

Closes #458

lib/features/rules/BpmnRules.js

@@ -360,7 +360,7 @@ function canDrop(element, target, position) {
   // and participants
   if (is(element, 'bpmn:FlowElement') || is(element, 'bpmn:DataAssociation')) {
     if (is(target, 'bpmn:FlowElementsContainer')) {
-      return isExpanded(target) !== false;
+      return isExpanded(target);
     }
 
     return isAny(target, [ 'bpmn:Participant', 'bpmn:Lane' ]);

lib/util/DiUtil.js

@@ -10,7 +10,7 @@ module.exports.isExpanded = function(element) {
   }
 
   if (is(element, 'bpmn:SubProcess')) {
-    return getBusinessObject(element).di.isExpanded;
+    return !!getBusinessObject(element).di.isExpanded;
   }
 
   if (is(element, 'bpmn:Participant')) {

test/spec/features/rules/BpmnRules.process.bpmn

@@ -21,6 +21,7 @@
     <bpmn2:dataObjectReference id="DataObjectReference" dataObjectRef="DataObject"/>
     <bpmn2:dataObject id="DataObject"/>
     <bpmn2:dataStoreReference id="DataStoreReference" name="" dataStoreRef="DataStore_1"/>
+    <bpmn2:subProcess id="CollapsedSubProcess"/>
     <bpmn2:textAnnotation id="TextAnnotation"/>
   </bpmn2:process>
   <bpmn2:dataStore id="DataStore_1" name="Data Store 1"/>
@@ -83,6 +84,9 @@
           <dc:Bounds height="21.0" width="79.0" x="657.0" y="216.0"/>
         </bpmndi:BPMNLabel>
       </bpmndi:BPMNShape>
+      <bpmndi:BPMNShape id="CollapsedSubProcess_di" bpmnElement="CollapsedSubProcess">
+        <dc:Bounds x="756" y="358" width="100" height="80"/>
+      </bpmndi:BPMNShape>
     </bpmndi:BPMNPlane>
   </bpmndi:BPMNDiagram>
 </bpmn2:definitions>

test/spec/features/rules/BpmnRulesSpec.js

@@ -102,6 +102,12 @@ describe('features/modeling/rules - BpmnRules', function() {
     }));
 
 
+    it('drop Start Event -> Collapsed Sub Process', function(){
+
+      expectCanDrop('StartEvent_None', 'CollapsedSubProcess', false);
+    });
+
+
     it('connect DataObjectReference -> StartEvent_None', inject(function() {
 
       expectCanConnect('DataObjectReference', 'StartEvent_None', {