--debug=topic yields error with thread_httpd

[triska]

My goal is to see debug messages on the console with the HTTP Unix daemon in combination with thread_httpd.

When I start with a very simple server template, server.pl:

:- use_module(library(http/thread_httpd)).
:- use_module(library(http/http_unix_daemon)).

:- initialization http_daemon.

Then I get among the help messages:

$ swipl server.pl --help
...
%   --debug=topic      Print debug message for topic
...

However, when I try to enable a debug topic, say, test, I get:

$ swipl server.pl -- --debug=test --port=8080 --interactive
Warning: test: no matching debug topic (yet)
ERROR: thread_create/3: Type error: `bool' expected, found `test' (an atom)