**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
"""Process form data."""
        conn_type = form.data['conn_type']
        conn_id = form.data["conn_id"]
        extra = {
            key: form.data[key]
            for key in self.extra_fields
            if key in form.data and key.startswith(f"extra__{conn_type}__")
        }
        
        
        extra_conn_params = form.data.get("extra")
        if extra_conn_params:
            try:
                extra.update(json.loads(extra_conn_params))
            except (JSONDecodeError, TypeError):
                flash(
                    Markup(
                        "<p>The <em>Extra</em> connection field contained an invalid value for Conn ID: "
                        f"<q>{conn_id}</q>.</p>"
                        "<p>If connection parameters need to be added to <em>Extra</em>, "
                        "please make sure they are in the form of a single, valid JSON object.</p><br>"
                        "The following <em>Extra</em> parameters were <b>not</b> added to the connection:<br>"
                        f"{extra_conn_params}",
                    ),
                    category="error",
                )
        if extra.keys():
            form.extra.data = json.dumps(extra)
    def prefill_form(self, form, pk):