**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
y_points = defaultdict(list)
        x_points = defaultdict(list)
        cumulative_y = defaultdict(list)
        task_instances = dag.get_task_instances_before(base_date, num_runs, session=session)
        if task_instances:
            min_date = task_instances[0].execution_date
        else:
            min_date = timezone.utc_epoch()
        ti_fails = (
            session.query(TaskFail)
            .filter(
                TaskFail.dag_id == dag.dag_id,
                TaskFail.execution_date >= min_date,
                TaskFail.execution_date <= base_date,
                TaskFail.task_id.in_([t.task_id for t in dag.tasks]),
            )
            .all()
        )
        fails_totals = defaultdict(int)
        for failed_task_instance in ti_fails:
            dict_key = (
                failed_task_instance.dag_id,
                failed_task_instance.task_id,
                failed_task_instance.execution_date,
            )
            if failed_task_instance.duration:
                fails_totals[dict_key] += failed_task_instance.duration
        for task_instance in task_instances:
            if task_instance.duration:
                date_time = wwwutils.epoch(task_instance.execution_date)