private static Logger getRootLogger() throws LogbackException {
        // org.slf4j.Logger.ROOT_LOGGER_NAME is fine. ch.qos.logback.classic.Logger.ROOT_LOGGER_NAME inherits slf4j's.
        final Logger logger = LoggerFactory.getLogger(Logger.ROOT_LOGGER_NAME);
        if (logger == null) {
            throw new NullPointerException("The root logger is unexpectedly null.");
        }
        if (!logger.getClass().getName().equals("ch.qos.logback.classic.Logger")) {
            throw new ClassCastException("The root logger is unexpectedly not ch.qos.logback.classic.Logger.");
        }
        return logger;
    }
Configures Logback's root logger.

<p>It calls Logback's configurators through reflection so that embulk-core does not need to depend on Logback's classes.
embulk-core/src/main/java/org/embulk/cli/CliLogbackConfigurator.java