pfa file required using residue-based fda_shortest_path

[BerndDoser]

I'm trying to use the fda_shortest_path module for the analysis with the following comand

gmx_fda fda_shortest_path -i output.pfr -s md.tpr -n index.ndx -o shortest.pdb

and I receive the following error message:

Fatal error:
Error opening file fda.pfa

If you notice from my input file, I performed the analysis residue-based and not atom-based, thus I only have an output.pfr file and not a out.pfa.
As a test, I created an empity fda.pfa file and the analysis work without printing anything in the output.
I suppose this could be due to a problem in the code because it seems the algo requires a specific file called fda.pfa

[BerndDoser]

Unfortunately, I cannot reproduce the issue with

cd src/gromacs/gmxana/fda/tests/data/glycine_trimer
gmx_fda fda_shortest_path -i fda.pfr -s glycine_trimer.pdb -n index.ndx -o shortest.pdb

[BerndDoser]

The issue was reproducible with special user data. Although the -diff option is not used, the program is trying to open a second pairwise forces file, which is not available.