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
task2 = DummyOperator(task_id="task2")
                task3 = DummyOperator(task_id="task3")
                task4 = DummyOperator(task_id="task4")
                task2 >> [task3, task4]
            task5 = DummyOperator(task_id="task5")
            task5 << group_b
        task1 >> group_a
        with TaskGroup("group_c") as group_c:
            task6 = DummyOperator(task_id="task6")
            task7 = DummyOperator(task_id="task7")
            task8 = DummyOperator(task_id="task8")
            [task6, task7] >> task8
            group_a >> group_c
        task5 >> task8
        task9 = DummyOperator(task_id="task9")
        task10 = DummyOperator(task_id="task10")
        group_c >> [task9, task10]
        with TaskGroup("group_d") as group_d:
            task11 = DummyOperator(task_id="task11")
            task12 = DummyOperator(task_id="task12")
            task11 >> task12
        group_d << group_c
    nodes = task_group_to_dict(dag.task_group)
    edges = dag_edges(dag)
    assert extract_node_id(nodes) == {
        'id': None,
        'children': [
            {
                'id': 'group_a',
                'children': [