[exim] Rewrite rule in Exim4

Hi,
I have a problem about a rewrite rule I configured.
Basically, I want to rewrite all emails from my stage-environment to
be sent to a particular mailbox.
So this is what I did for rewriting:

^.*\$ "${if match {$header_From:}{.*@stage.domain.tld} {user@???}}" tT

It works as planned, but I get nasty errors in my paniclog for all
other mails:

2016-08-29 09:48:10 XXX Rewrite of other-user@??? yielded
unparseable address: empty address in address

What can I do to get rid of this message?

Kind regards,

Roland