fix: remove default start event for ad-hoc subprocess (#2295)

Related to camunda/camunda-modeler#4858

Author: Buckwich

lib/features/modeling/behavior/SubProcessStartEventBehavior.js

@@ -26,6 +26,7 @@ export default function SubProcessStartEventBehavior(injector, modeling) {
 
     if (
       !is(newShape, 'bpmn:SubProcess') ||
+      is(newShape,'bpmn:AdHocSubProcess') ||
       ! (is(oldShape, 'bpmn:Task') || is(oldShape, 'bpmn:CallActivity')) ||
       !isExpanded(newShape)
     ) {

test/spec/features/modeling/behavior/SubProcessStartEventBehaviorSpec.js

@@ -74,6 +74,30 @@ describe('features/modeling/behavior - subprocess start event', function() {
     });
 
 
+    describe('task -> adhoc subprocess', function() {
+
+      it('should NOT add start event child to adhoc subprocess', inject(
+        function(elementRegistry, bpmnReplace) {
+
+          // given
+          var task = elementRegistry.get('Task_1'),
+              collapsedSubProcess,
+              startEvents;
+
+          // when
+          collapsedSubProcess = bpmnReplace.replaceElement(task, {
+            type: 'bpmn:AdHocSubProcess',
+            isExpanded: true
+          });
+
+          // then
+          startEvents = getChildStartEvents(collapsedSubProcess);
+
+          expect(startEvents).to.have.length(0);
+        }));
+    });
+
+
     describe('task -> collapsed subprocess', function() {
 
       it('should NOT add start event child to subprocess', inject(