postfix/nqmgr warning ! (?)

First of all , my config :
I have a Mail server with postfix + amavisd-new + clamav + spamassasin on a
redhat 8.0.
All seems to be ok now (but it was a nightmare to configure).

Clamav reject the infected mails and send a mail to administrator with the
info.
Freshclamd check regulary if a new virus definition is available.
Spamassassin intercept (depending on the settings of course) the spam and
send a mail to the administrator with the details.

The problem :
In may /var/log/maillog file I get this warning :
postfix/nqmgr[682]: warning : connect to transport clamscan: No such file or
directory

But all seem to work correctly.
Any idea or a direction to search ?

Thanks in advance.