### Apache Airflow version

2.6.0

### What happened

When clicking the "Trigger DAG w/ config" in a DAG UI I receive a 500 "Oops" page when `params` are defined for the DAG.

The Airflow webserver logs show this:

```
2023-05-02T13:02:50 - [2023-05-02T12:02:50.249+0000] {app.py:1744} ERROR - Exception on /trigger [GET]
2023-05-02T13:02:50 - Traceback (most recent call last):
2023-05-02T13:02:50 -   File "/opt/airflow/.local/lib/python3.10/site-packages/flask/app.py", line 2529, in wsgi_app
2023-05-02T13:02:50 -     response = self.full_dispatch_request()
2023-05-02T13:02:50 -   File "/opt/airflow/.local/lib/python3.10/site-packages/flask/app.py", line 1825, in full_dispatch_request
2023-05-02T13:02:50 -     rv = self.handle_user_exception(e)
2023-05-02T13:02:50 -   File "/opt/airflow/.local/lib/python3.10/site-packages/flask/app.py", line 1823, in full_dispatch_request
2023-05-02T13:02:50 -     rv = self.dispatch_request()
2023-05-02T13:02:50 -   File "/opt/airflow/.local/lib/python3.10/site-packages/flask/app.py", line 1799, in dispatch_request
2023-05-02T13:02:50 -     return self.ensure_sync(self.view_functions[rule.endpoint])(**view_args)
2023-05-02T13:02:50 -   File "/opt/airflow/.local/lib/python3.10/site-packages/airflow/www/auth.py", line 47, in decorated
2023-05-02T13:02:50 -     return func(*args, **kwargs)
2023-05-02T13:02:50 -   File "/opt/airflow/.local/lib/python3.10/site-packages/airflow/www/decorators.py", line 125, in wrapper
2023-05-02T13:02:50 -     return f(*args, **kwargs)
2023-05-02T13:02:50 -   File "/opt/airflow/.local/lib/python3.10/site-packages/airflow/utils/session.py", line 76, in wrapper
2023-05-02T13:02:50 -     return func(*args, session=session, **kwargs)
2023-05-02T13:02:50 -   File "/opt/airflow/.local/lib/python3.10/site-packages/airflow/www/views.py", line 1967, in trigger
2023-05-02T13:02:50 -     return self.render_template(
2023-05-02T13:02:50 -   File "/opt/airflow/.local/lib/python3.10/site-packages/airflow/www/views.py", line 640, in render_template
2023-05-02T13:02:50 -     return super().render_template(
2023-05-02T13:02:50 -   File "/opt/airflow/.local/lib/python3.10/site-packages/flask_appbuilder/baseviews.py", line 339, in render_template
2023-05-02T13:02:50 -     return render_template(
2023-05-02T13:02:50 -   File "/opt/airflow/.local/lib/python3.10/site-packages/flask/templating.py", line 147, in render_template
2023-05-02T13:02:50 -     return _render(app, template, context)
2023-05-02T13:02:50 -   File "/opt/airflow/.local/lib/python3.10/site-packages/flask/templating.py", line 130, in _render
2023-05-02T13:02:50 -     rv = template.render(context)
2023-05-02T13:02:50 -   File "/opt/airflow/.local/lib/python3.10/site-packages/jinja2/environment.py", line 1301, in render
2023-05-02T13:02:50 -     self.environment.handle_exception()
2023-05-02T13:02:50 -   File "/opt/airflow/.local/lib/python3.10/site-packages/jinja2/environment.py", line 936, in handle_exception
2023-05-02T13:02:50 -     raise rewrite_traceback_stack(source=source)
2023-05-02T13:02:50 -   File "/opt/airflow/.local/lib/python3.10/site-packages/airflow/www/templates/airflow/trigger.html", line 106, in top-level template code
2023-05-02T13:02:50 -     <span class="help-block">{{ form_details.description }}</span>
2023-05-02T13:02:50 -   File "/opt/airflow/.local/lib/python3.10/site-packages/airflow/www/templates/airflow/main.html", line 21, in top-level template code
2023-05-02T13:02:50 -     {% from 'airflow/_messages.html' import show_message %}
2023-05-02T13:02:50 -   File "/opt/airflow/.local/lib/python3.10/site-packages/flask_appbuilder/templates/appbuilder/baselayout.html", line 2, in top-level template code
2023-05-02T13:02:50 -     {% import 'appbuilder/baselib.html' as baselib %}
2023-05-02T13:02:50 -   File "/opt/airflow/.local/lib/python3.10/site-packages/flask_appbuilder/templates/appbuilder/init.html", line 42, in top-level template code
2023-05-02T13:02:50 -     {% block body %}
2023-05-02T13:02:50 -   File "/opt/airflow/.local/lib/python3.10/site-packages/flask_appbuilder/templates/appbuilder/baselayout.html", line 19, in block 'body'
2023-05-02T13:02:50 -     {% block content %}
2023-05-02T13:02:50 -   File "/opt/airflow/.local/lib/python3.10/site-packages/airflow/www/templates/airflow/trigger.html", line 162, in block 'content'
2023-05-02T13:02:50 -     {{ form_element(form_key, form_details) }}
2023-05-02T13:02:50 -   File "/opt/airflow/.local/lib/python3.10/site-packages/jinja2/runtime.py", line 777, in _invoke
2023-05-02T13:02:50 -     rv = self._func(*arguments)
2023-05-02T13:02:50 -   File "/opt/airflow/.local/lib/python3.10/site-packages/airflow/www/templates/airflow/trigger.html", line 83, in template
2023-05-02T13:02:50 -     {%- for txt in form_details.value -%}
2023-05-02T13:02:50 - TypeError: 'NoneType' object is not iterable
```

### What you think should happen instead

No error is shown (worked in 2.5.2)

### How to reproduce

Create a DAG with the following config defined for parameters:

```
params={
            "delete_actions": Param(
                False,
                description="Whether to delete actions after execution.",
                type="boolean",
            ),
            "dates": Param(
                None,
                description="An explicit list of date strings to run on.",
                type=["null", "array"],
                minItems=1,
            ),
            "start_date_inclusive": Param(
                None,
                description="An inclusive start-date used to generate a list of dates to run on.",
                type=["null", "string"],
                pattern="^[0-9]{4}[-/][0-9]{2}[-/][0-9]{2}$",
            ),
            "end_date_exclusive": Param(
                None,
                description="An exclusive end-date used to generate a list of dates to run on.",
                type=["null", "string"],
                pattern="^[0-9]{4}[-/][0-9]{2}[-/][0-9]{2}$",
            ),
            "actions_bucket_name": Param(
                None,
                description='An S3 bucket to read batch actions from. Set as "ACTIONS_BUCKET".',
                type=["null", "string"],
            ),
            "actions_path_prefix": Param(
                None,
                description='An S3 bucket to read batch actions from. Prefixes "ACTIONS_PATH".',
                type=["null", "string"],
                pattern="^.+/$",
            ),
            "sns_output_topic_name": Param(
                None,
                description='An SNS output topic ARN to set as "DATA_READY_TO_INDEX_OUTPUT_TOPIC."',
                type=["null", "string"],
            ),
        },
        # required to convert params to their correct types
        render_template_as_native_obj=True,
```

Deploy the DAG, click the manual trigger button.

### Operating System

Debian

### Versions of Apache Airflow Providers

N/A

### Deployment

Other Docker-based deployment

### Deployment details

Amazon ECS
Python version: 3.10.11
Airflow version: 2.6.0 (official docker image as base)

### Anything else

Occurs every time.

Does *NOT* occur when `params` are not defined on the DAG.

### 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)

#
#
#
from __future__ import annotations
import datetime
import json
import pytest
from airflow.models import DagBag, DagRun
from airflow.models.param import Param
from airflow.operators.empty import EmptyOperator
from airflow.security import permissions
from airflow.utils import timezone
from airflow.utils.session import create_session
from airflow.utils.types import DagRunType
from tests.test_utils.api_connexion_utils import create_test_client
from tests.test_utils.www import check_content_in_response
@pytest.fixture(scope="function", autouse=True)
def initialize_one_dag():