**Apache Airflow version**: 2.1.0

**Browsers**: Chrome and Firefox

**What happened**:

Before upgrading to 2.1.0

![before](https://user-images.githubusercontent.com/14293802/120359517-c1ca1100-c2d5-11eb-95ba-58ccc0a3ac37.png)

After upgrading to 2.1.0

![after](https://user-images.githubusercontent.com/14293802/120359528-c4c50180-c2d5-11eb-8e04-f34846ea2736.png)

**What you expected to happen**:

Show/Edit/Delete under Security -> Users are available

<!-- What do you think went wrong? -->

**How to reproduce it**:

Go to Security -> Users (as an admin of course) 
airflow/www/views.py
'dag_id': r.dag_id,
                'execution_date': r.execution_date.isoformat(),
                'start_date': r.start_date.isoformat(),
            }
            for r in query
        }
        return wwwutils.json_response(resp)
    @expose('/code')
    @auth.has_access(
        [
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_DAG),
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_DAG_CODE),
        ]
    )
    @provide_session
    def code(self, session=None):
        """Dag Code."""
        all_errors = ""
        dag_orm = None
        dag_id = None
        try:
            dag_id = request.args.get('dag_id')
            dag_orm = DagModel.get_dagmodel(dag_id, session=session)
            code = DagCode.get_code_by_fileloc(dag_orm.fileloc)
            html_code = Markup(highlight(code, lexers.PythonLexer(), HtmlFormatter(linenos=True)))
        except Exception as e:
            all_errors += (
                "Exception encountered during "
                + f"dag_id retrieval/dag retrieval fallback/code highlighting:\n\n{e}\n"
            )