code: @Deployment public void testChangingCollection(){
    Map<String,Object> vars=new HashMap<String,Object>();
    vars.put("multi_users",Arrays.asList("testuser"));
    ProcessInstance instance=runtimeService.startProcessInstanceByKey("test_multi",vars);
    assertNotNull(instance);
    Task task=taskService.createTaskQuery().singleResult();
    assertEquals("multi",task.getTaskDefinitionKey());
    vars.put("multi_users",new ArrayList<String>());
    taskService.complete(task.getId(),vars);
    List<ProcessInstance> instances=runtimeService.createProcessInstanceQuery().list();
    assertEquals(0,instances.size());
  }
  