Airflow v2.0b3
 Kubernetes v1.19.3

Discovered issue while testing KubernetesPodOperator (haven't tested with other operator).
If I create a multiline string using """ """", add some variables inside (Jinja templating), then use this string as an argument to KubernetesPodOperator:
- In Graph View DAG is not visible (just gray area where it should be a digraph);
- in browser's web console i see the following error:

`Uncaught TypeError: node is undefined
    preProcessGraph http://localhost:8080/static/dist/dagre-d3.min.js:103
    preProcessGraph http://localhost:8080/static/dist/dagre-d3.min.js:103
    fn http://localhost:8080/static/dist/dagre-d3.min.js:103
    call http://localhost:8080/static/dist/d3.min.js:3
    draw http://localhost:8080/graph?dag_id=mydag&execution_date=mydate
    expand_group http://localhost:8080/graph?dag_id=mydag&execution_date=mydate
    <anonymous> http://localhost:8080/graph?dag_id=mydag&execution_date=mydate`

Tree view works without issues in this case. The DAG succeeds.
tests/utils/test_task_group.py
return "task_2"
    @task
    def task_3():
        return "task_3"
    @task
    def task_4(task_2_output, task_3_output):
        print(task_2_output, task_3_output)
    @task
    def task_5():
        print("task_5")
    execution_date = pendulum.parse("20200101")
    with DAG("test_build_task_group_with_task_decorator", start_date=execution_date) as dag:
        tsk_1 = task_1()
        with TaskGroup("group234") as group234:
            tsk_2 = task_2()
            tsk_3 = task_3()
            tsk_4 = task_4(tsk_2, tsk_3)
        tsk_5 = task_5()
        tsk_1 >> group234 >> tsk_5
    
    assert tsk_1.operator in tsk_2.operator.upstream_list
    assert tsk_1.operator in tsk_3.operator.upstream_list
    assert tsk_5.operator in tsk_4.operator.downstream_list
    
    assert extract_node_id(task_group_to_dict(dag.task_group)) == {
        'id': None,
        'children': [
            {
                'id': 'group234',
                'children': [