Thanks for the report. I've added the following doc for the next release...
=head2 noop
Example:
$imap->noop or die "noop failed: $@\n";
The B<noop> method performs an IMAP NOOP command. Per RFC3501 this
command does nothing and always succeeds. However, if a connection
times out or other errors occur while communicating with the server,
this method can still fail. This command can be used as a periodic
poll to check for (untagged) status updates (new messages, etc.) from
the server and also to reset any inactivity/auto-logout timers the
server may maintain.