Thanks for your reply.
I tried it out and it works well.

What I want to ask you is, if there is a way to change the default value of the string parameters (e.g. in the firebird.conf), because I would like to do that on the server of my customer, to fix this problem without having to install an update of my program. Have to test several parts of the new version, before I can release it.

So it would be great to have a workaround for this problem without change the sql statements used in my prgram.