When user_name is stored as None (e.g. Telegram users without a
display name), dict.get('user_name', '') returns None because the
key exists — the default is only used for missing keys. This causes
a TypeError when the format specifier :<20 is applied to None.
Use `or ''` to coerce None to an empty string.
Fixes#7392
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>