public void guess(final ConfigSource configSource, final String outputPathString) {
        final Path outputPath = (outputPathString == null ? null : Paths.get(outputPathString));
        try {
            guessInternal(configSource, outputPath);
        } catch (IOException ex) {
            throw new RuntimeException(ex);
        }
    }
Runs the guess subcommand.

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