public void guess(final String configFilePathString, final String outputPathString) {
        final Path outputPath = (outputPathString == null ? null : Paths.get(outputPathString));
        guess(Paths.get(configFilePathString), outputPath);
    }
Runs the guess subcommand.

It receives Strings as parameters to be called from Ruby (embulk/runner.rb).
embulk-core/src/main/java/org/embulk/EmbulkRunner.java