When only a message argument is given to the crash manager, the popup display
"Error while validating constarint" and "None" with the warning message
which does not make any sense for the common user.
Do not restrict followers-based alias to members of non public channels.
Otherwise you may have issues defining a public mailing list with a
subscription step. People still wouldn't be able to post on a public
channel using a restricted alias.
Now that channels can follow documents, restricted aliases are a bit too
restricted. We consider that followers-based aliases accept emails from
the direct followers (message_partner_ids) or member of non public
channels (message_channel_ids, filetered public field). This way we avoid
having public channels added by mistake, leading to information leak.
Kinjal Mehta