### Apache Airflow version

2.5.1

### What happened

/calendar page give a problem, here is the capture



![屏幕截图 2023-01-30 093116](https://user-images.githubusercontent.com/19165258/215369479-9fc7de5c-f190-460c-9cf7-9ab27d8ac355.png)


### What you think should happen instead

_No response_

### How to reproduce

_No response_

### Operating System

Ubuntu 22.04.1 LTS

### Versions of Apache Airflow Providers

Distributor ID: Ubuntu
Description:    Ubuntu 22.04.1 LTS
Release:        22.04
Codename:       jammy

### Deployment

Other

### Deployment details


Distributor ID: Ubuntu
Description:    Ubuntu 22.04.1 LTS
Release:        22.04
Codename:       jammy

### Anything else

_No response_

### Are you willing to submit PR?

- [ ] 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)

"""Prefill the form."""
        try:
            extra = form.data.get("extra")
            if extra is None:
                extra_dictionary = {}
            else:
                extra_dictionary = json.loads(extra)
        except JSONDecodeError:
            extra_dictionary = {}
        if not isinstance(extra_dictionary, dict):
            logging.warning("extra field for %s is not a dictionary", form.data.get("conn_id", "<unknown>"))
            return
        for field_key in self.extra_fields:
            field_name = self.extra_field_name_mapping[field_key]
            value = extra_dictionary.get(field_name, "")
            if not value:
                
                value = extra_dictionary.get(field_key, "")
            if value:
                field = getattr(form, field_key)
                field.data = value
class PluginView(AirflowBaseView):