**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
"""Get Execution Data, Base Date & Number of runs from a Request"""
    date_time = www_request.args.get('execution_date')
    if date_time:
        date_time = timezone.parse(date_time)
    else:
        date_time = dag.get_latest_execution_date(session=session) or timezone.utcnow()
    base_date = www_request.args.get('base_date')
    if base_date:
        base_date = timezone.parse(base_date)
    else:
        
        
        base_date = (date_time + timedelta(seconds=1)).replace(microsecond=0)
    default_dag_run = conf.getint('webserver', 'default_dag_run_display_number')
    num_runs = www_request.args.get('num_runs', default=default_dag_run, type=int)
    drs = (
        session.query(DagRun)
        .filter(DagRun.dag_id == dag.dag_id, DagRun.execution_date <= base_date)
        .order_by(desc(DagRun.execution_date))
        .limit(num_runs)
        .all()
    )
    dr_choices = []
    dr_state = None
    for dr in drs:
        dr_choices.append((dr.execution_date.isoformat(), dr.run_id))
        if date_time == dr.execution_date: