User objects username attribute is not populated

[Arbiter-S]

Code that causes the issue

GPs_list = [1234567891]
@client.on(events.NewMessage(chats=GPs_list))
async def handler(event):
    user = await event.get_sender()
    print(user.username)

client.start()
client.run_until_disconnected()

Expected behavior

User objects to have username attribute populated.

Actual behavior

Users have None as their username.

Traceback

None

Telethon version

1.37.0

Python version

3.12.4

Operating system (including distribution name and version)

Windows 11

Other details

I checked this with another 3rd party client named Plus and users did have usernames visible to my account. It might help to mention the group has their members list hidden.

Checklist

• [X] The error is in the library's code, and not in my own.
• [X] I have searched for this issue before posting it and there isn't an open duplicate.
• [X] I ran pip install -U https://github.com/LonamiWebs/Telethon/archive/v1.zip and triggered the bug in the latest version.