[Exim] warn with no log message?

I have several warn statements to set up acl variables, one in
particular is logging an annoying line "Warning: Unrouteable address"
every time the condition fails:

warn    domains = +local_domains
                 !verify = recipient
                 set acl_c0 = ${eval: $acl_c0+1}
                 delay = ${eval: ($acl_c0 - 1) * 60}s

I have tried to suppress the message by explicitly adding an empty log message

        log_message =

but this does not work.

Note that this statements are part of an ACL that is called indirectly as in

warn acl = aclname

Is there any way to suppress these messages?
If not can I propose that either the log_message can be set
explicitly to nothing or that a new verb, like "evaluate", be
introduced, which will not generate any message but just evaluate its
conditions in order until one is found false and then continue to the
next statement?

Or is it all there already?

Thanks

Giuliano
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