[exim] tainted filname issue

I just upgraded to 4.94.2, and most everything is working fine. But I'm
getting an issue on DKIM signings with tainted filename. I looked over
the list and tried to apply the same fix I've seen used before, but I
guess I'm not understanding it. Here's my dkim_private_key statement:

  dkim_private_key   = ${if
exists{/etc/exim/DKIM/${lc:$sender_address_domain}/dkim.private.key.pem}\
{/etc/exim/DKIM/${lc:$sender_address_domain}/dkim.private.key.pem}{0}}

So how do I correct this? Thanks!

--
Dan Egli
From my Test Server