I believe you've discovered a bug in Config::General. On line 519, it says:

my @files = sort grep { -f catfile($configfile, $_) } catfile($configf
+ile, $_), readdir INCLUDEDIR;
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And the extra catfile($configfile, $_), doesn't make sense to me. I think the line should be:

my @files = sort grep { -f catfile($configfile, $_) } readdir INCLUDED
+IR;
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You should probably file a bug report, but note the module hasn't had a release in about 5 years, so you'll have to decide whether you might want to patch the module yourself.

Update: Thanks for reporting it as RT#139261