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.
airflow/models/baseoperator.py
"""Stringified DAGs and operators contain exactly these fields."""
        if not cls.__serialized_fields:
            from airflow.models.dag import DagContext
            
            
            
            
            DagContext.push_context_managed_dag(None)
            cls.__serialized_fields = frozenset(
                vars(BaseOperator(task_id='test')).keys()
                - {
                    'inlets',
                    'outlets',
                    '_upstream_task_ids',
                    'default_args',
                    'dag',
                    '_dag',
                    '_BaseOperator__instantiated',
                }
                | {
                    '_task_type',
                    'subdag',
                    'ui_color',
                    'ui_fgcolor',
                    'template_fields',
                    'template_fields_renderers',
                }