IMHO, you should try to make this platform independent, look at File::Basename or use $^O.

here:

sub _load_reference_if_you_need { # {{{
    if ($reference) {
        # Reference already loaded or initialized.
        return $reference;
    }

    # Is there a reference file?
    if (not -f $default_reference_filename) {
        # Nope. Warn the User, but don't make a tragedy of it.
        diag("No reference file found. All calls to is_referenced_ok W
+ILL fail.");

        return $reference = {};
    }

    return $reference = $serializer_load->($default_reference_filename
+);
}
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I'd also check if you have read permissions and wrap the call to the serializer in an eval so you can catch any error in the serializer.