% cat bogus.svg
<svg viewBox="0 0 1 1"><defs><g id="a"></g></defs><use xlink:href="#a"/></svg>
% rm -f bogus.pdf
% rsvg-convert -f pdf -o bogus.pdf bogus.svg
Error reading SVG:XML parse error: error code=201 (3) in (null):1:71: Namespace prefix xlink for href on use is not defined


% ls -la bogus.*
-rw------- 1 frank frank  0 16. Sep 05:07 bogus.pdf
-rw------- 1 frank frank 79 16. Sep 05:06 bogus.svg
%

The error itself is correct AFAIK, but the location is given with
"(null)" instead of the correct filename.

Afterwards, an empty output file is left which can be problematic
e.g. when run from a makefile. Of course, it can be worked around
with something like '|| { rm -f "$@"; false; }', but that really
shouldn't be necessery.