An exception occurred when running demo/ui.

After running uv run main.py in the command line, the following message appeared:

`(A2A) PS E:\Files\AI\A2A\demo\ui> uv run main.py
warning: `VIRTUAL_ENV=E:\Files\AI\A2A\.venv` does not match the project environment path `.venv` and will be ignored; use `--active` to target the active environment instead
INFO: Started server process [35056]
INFO: Waiting for application startup.
INFO: Application startup complete.
INFO: Uvicorn running on http://0.0.0.0:12000 (Press CTRL+C to quit)`

However, when I accessed http://127.0.0.1:12000/ in the browser, the following error occurred:

`(A2A) PS E:\Files\AI\A2A\demo\ui> uv run main.py
warning: `VIRTUAL_ENV=E:\Files\AI\A2A\.venv` does not match the project environment path `.venv` and will be ignored; use `--active` to target the active environment instead
INFO: Started server process [35056]
INFO: Waiting for application startup.
INFO: Application startup complete.
INFO: Uvicorn running on http://0.0.0.0:12000 (Press CTRL+C to quit)
INFO: 127.0.0.1:13400 - "GET / HTTP/1.1" 200 OK
INFO: 127.0.0.1:13400 - "GET /styles.css HTTP/1.1" 304 Not Modified
INFO: 127.0.0.1:13402 - "GET /zone.js/bundles/zone.umd.js HTTP/1.1" 304 Not Modified
INFO: 127.0.0.1:13403 - "GET /prod_bundle.js HTTP/1.1" 304 Not Modified
INFO: 127.0.0.1:13402 - "POST /__ui__ HTTP/1.1" 200 OK
INFO: 127.0.0.1:13402 - "GET /__web-components-module__/components/async_poller.js HTTP/1.1" 304 Not Modified
INFO: 127.0.0.1:13402 - "POST /__ui__ HTTP/1.1" 200 OK
Failed to list conversations: Server disconnected without sending a response.
Failed to list tasks Server disconnected without sending a response.
Failed to update state: 'NoneType' object is not iterable
Traceback (most recent call last):
File "E:\Files\AI\A2A\demo\ui\state\host_agent_service.py", line 154, in UpdateAppState
for task in await GetTasks():
^^^^^^^^^^^^^^^^
TypeError: 'NoneType' object is not iterable
INFO: 127.0.0.1:13402 - "POST /__ui__ HTTP/1.1" 200 OK
Failed to list conversations:
Failed to list tasks Server disconnected without sending a response.
Failed to update state: 'NoneType' object is not iterable
Traceback (most recent call last):
File "E:\Files\AI\A2A\demo\ui\state\host_agent_service.py", line 154, in UpdateAppState
for task in await GetTasks():
^^^^^^^^^^^^^^^^
TypeError: 'NoneType' object is not iterable
INFO: 127.0.0.1:13402 - "POST /__ui__ HTTP/1.1" 200 OK
Failed to list conversations: Server disconnected without sending a response.
Failed to list tasks Server disconnected without sending a response.
Failed to update state: 'NoneType' object is not iterable`

**How should I resolve this issue, and what troubleshooting approach should I take?**