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
"""Required by TaskMixin"""
        return [self]
    @property
    def leaves(self) -> List["BaseOperator"]:
        """Required by TaskMixin"""
        return [self]
    def _set_relatives(
        self,
        task_or_task_list: Union[TaskMixin, Sequence[TaskMixin]],
        upstream: bool = False,
    ) -> None:
        """Sets relatives for the task or task list."""
        if not isinstance(task_or_task_list, Sequence):
            task_or_task_list = [task_or_task_list]
        task_list: List["BaseOperator"] = []
        for task_object in task_or_task_list:
            task_object.update_relative(self, not upstream)
            relatives = task_object.leaves if upstream else task_object.roots
            task_list.extend(relatives)
        for task in task_list:
            if not isinstance(task, BaseOperator):
                raise AirflowException(
                    "Relationships can only be set between "
                    "Operators; received {}".format(task.__class__.__name__)
                )