    @Test
    public void taskEnd_noModel() {

        when(handler.removeOrCreate(task, info)).thenReturn(model);
        assist.taskEnd(task, EndCause.COMPLETED, null);
        verify(callback).taskEnd(eq(task), eq(EndCause.COMPLETED), nullable(Exception.class),
                any(Listener4Assist.Listener4Model.class));
    }