BUG #4794: server closed the connection unexpectedly

The following bug has been logged online:

Bug reference:      4794
Logged by:          Markus Meyer
Email address:      markus@7val.com
PostgreSQL version: 8.3.3
Operating system:   Debian 2.6.22.19-vs2.2.0.7
Description:        server closed the connection unexpectedly
Details:

If i make an

SELECT xmlconcat(('<datanode>' || NULL || '</datanode>')::xml);

follows

server closed the connection unexpectedly
        This probably means the server terminated abnormally
        before or while processing the request.