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
"""Getting the content of files for template_field / template_ext"""
        if self.template_ext:  
            for field in self.template_fields:
                content = getattr(self, field, None)
                if content is None:  
                    continue
                elif isinstance(content, str) and any(content.endswith(ext) for ext in self.template_ext):
                    env = self.get_template_env()
                    try:
                        setattr(self, field, env.loader.get_source(env, content)[0])
                    except Exception as e:  
                        self.log.exception(e)
                elif isinstance(content, list):
                    env = self.dag.get_template_env()
                    for i in range(len(content)):  
                        if isinstance(content[i], str) and any(
                            content[i].endswith(ext) for ext in self.template_ext
                        ):
                            try:
                                content[i] = env.loader.get_source(env, content[i])[0]
                            except Exception as e:  
                                self.log.exception(e)
        self.prepare_template()
    @property
    def upstream_list(self) -> List["BaseOperator"]: