docs: @Override
     public InputStream lookupFileStrict(String filename, ClassLoader cl) throws FileNotFoundException {
        InputStream is = filename == null || filename.length() == 0 ? null : getAsInputStreamFromClassLoader(filename, cl);
        if (is == null) {
           if (log.isDebugEnabled())
              log.debugf("Unable to find file %s in classpath; searching for this file on the filesystem instead.", filename);
           return new FileInputStream(filename);
        }
        return is;
     }