bug#74658: Remove the Mail-Followup-To header when empty

[Robert Pluim <rpluim@gmail.com>]

>>>>> On Tue, 03 Dec 2024 00:17:10 +0100, Tomas Volf <~@wolfsden.cz> said:

    Tomas> Tags: patch
    Tomas> According to the info manual (message)Mailing Lists, the
    Tomas> Mail-Followup-To header should be removed when it is empty:

    >> If there is one, it is left alone.  (Except if it’s empty; in that
    >> case, the field is removed and is not replaced with an automatically
    >> generated one.  This lets you disable MFT generation on a per-message
    >> basis.)

    Tomas> While the code attempted to do that, the call to `message-remove-header'
    Tomas> passed wrong arguments.  Since the IS-REGEXP argument was not passed,
    Tomas> the HEADER was considered a full header name (if I read the code right)
    Tomas> and therefore failed to match (since the code passed in a regexp instead
    Tomas> of a fixed string).

    Tomas> The fix is simple, remove the leading ^ and trailing :.

Yep. I can apply this to master. Maintainers, is adding
Copyright-paperwork-exempt: yes enough here? Or do we need a copyright
assignment from Tomas?

Robert
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