fix(mailing): don't default to empty string for smtp_password and user, since mailing lib only expects None as empty values

rhodecode/lib/celerylib/tasks.py

@@ -1,4 +1,4 b''
-# Copyright (C) 2012-2023 RhodeCode GmbH
+# Copyright (C) 2012-2024 RhodeCode GmbH
 #
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU Affero General Public License, version 3
@@ -64,8 +64,9 b' def send_email(recipients, subject, body'
                   "Make sure that `smtp_server` variable is configured "
                   "inside the .ini file")
         return False
-
-    subject = "%s %s" % (email_config.get('email_prefix', ''), subject)
+    conf_prefix = email_config.get('email_prefix', None)
+    prefix = f'{conf_prefix} ' if conf_prefix else ''
+    subject = f"{prefix}{subject}"
 
     if recipients:
         if isinstance(recipients, str):
@@ -86,8 +87,8 b' def send_email(recipients, subject, body'
     email_conf = dict(
         host=mail_server,
         port=email_config.get('smtp_port', 25),
-        username=email_config.get('smtp_username'),
-        password=email_config.get('smtp_password'),
+        username=email_config.get('smtp_username', None),
+        password=email_config.get('smtp_password', None),
 
         tls=str2bool(email_config.get('smtp_use_tls')),
         ssl=str2bool(email_config.get('smtp_use_ssl')),