deal with empty sender name field

screenless/bureau/mailroom/mailroom.py

@@ -303,6 +303,8 @@ class MailRoom(Bureau):
 
             msg.msgid = str(msgid)
             sender = envelope.from_[0]
+            if sender.name is None:
+                sender.name = b""
             msg.fromaddr = sender.mailbox + b"@" + sender.host
             msg.fromaddr = clean_header(msg.fromaddr.decode("utf-8"))
             msg.fromname = clean_header(sender.name.decode("utf-8"))