Unable to extract regexes

[phreppo]

OS: Ubuntu 20.04

I cloned the repository and set the environment variable VULN_REGEX_DETECTOR_ROOT to the repo root and I also ran the configure script.
Then, I try to run the analysis on one Python file located in bin/test/check-file:

cd bin/test/check-file
../../check-file.pl py-desc-1.json

The result is:

Extracting regexes
/home/my-name/vuln-regex-detector/src/extract/extract-regexes.pl /tmp/check-file-21009.json 2>>/tmp/check-file-21009-progress.log
{"couldExtractRegexes":0,"file":"t.py"}

I also tried to analyze repositories with check-tree.pl and check-repo.pl, but the results always include "couldExtractRegexes":0.
I didn't modify any files from the repo.
How can I solve this? Thanks!