Exception when trying to send email to user without an UNIX ID

[slacmshankar]

$ id mfrawnak
id: mfrawnak: no such user

INFO:main:Found templates ['UserAccount_NotActedOn_czar.jinja2', 'UserAccount_NotActedOn_user.jinja2']
ERROR:strawberry.execution:can only join an iterable

GraphQL request:2:3
1 | mutation requestNewSDFAccount($request: CoactRequestInput!) {
2 | requestNewSDFAccount(request: $request) {
| ^
3 | Id
Traceback (most recent call last):
.....
File "/app/schema.py", line 665, in requestNewSDFAccount
info.context.notify( this_req )
File "/app/main.py", line 225, in notify
return self.email.notify( request_type=request_type, request_status=request_status, data=self.db.to_dict(request), template_prefix=template_prefix, user=user_email, czars=czar_emails, skip_czar_emails=skip_czar_emails )
File "/app/main.py", line 487, in notify
email = self.create( to, f'{req_type} {status}', body, cc=cc, bcc=bcc )
File "/app/main.py", line 443, in create
email["To"] = ', '.join(to)
TypeError: can only join an iterable