[exim] Alias-Error to /dev/null

Hi Folks,

our /etc/aliases contains an Alias that is piped to a script:

bla: "|/path/to/script.pl"

Sometimes this script produces an error. sometimes....
Unfortunately a fix (which would be the best solution) is not the easiest.
Is there any way to pipe a possible error message to /dev/null ?

I tried

bla: "|/path/to/script.pl 2> /dev/null"

but now all output is send to /dev/null, but only possible errors should
land there.

Any ideas ?

Regards
Sascha