### Apache Airflow version

2.4.2

### What happened

Create a DAG and set the schedule parameter using a CronTriggerTimeTable instance. Enable the DAG so that there is DAG run data. Try to access the Calendar View for the DAG. An ERR_EMPTY_RESPONSE error is displayed instead of the page.

The Calendar View is accessible for other DAGs  that are using the schedule_interval set to a cron string instead.

### What you think should happen instead

The Calendar View should have been displayed.

### How to reproduce

Create a DAG and set the schedule parameter to a CronTriggerTimeTable instance. Enable the DAG and allow some DAG runs to occur. Try to access the Calender View for the DAG.

### Operating System

Red Hat Enterprise Linux 8.6

### Versions of Apache Airflow Providers

_No response_

### Deployment

Virtualenv installation

### Deployment details

Airflow 2.4.2 installed via pip with Python3.9 to venv using constraints.

### Anything else

_No response_

### Are you willing to submit PR?

- [X] Yes I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

selected_conn.login,
                    selected_conn.password,
                    selected_conn.schema,
                    selected_conn.port,
                    selected_conn.extra,
                )
                try:
                    session.add(dup_conn)
                    session.commit()
                    flash(f"Connection {new_conn_id} added successfully.", "success")
                except IntegrityError:
                    flash(
                        f"Connection {new_conn_id} can't be added. Integrity error, "
                        f"probably unique constraint.",
                        "warning",
                    )
                    session.rollback()
        self.update_redirect()
        return redirect(self.get_redirect())
    def process_form(self, form, is_created):
        """Process form data."""
        conn_id = form.data["conn_id"]
        conn_type = form.data["conn_type"]
        
        
        
        extra = {}
        extra_json = form.data.get("extra")
        if extra_json:
            try: