private static Throwable pickupException(final ReflectiveOperationException cause) {
            if (cause instanceof InvocationTargetException) {
                return ((InvocationTargetException) cause).getTargetException();
            } else {
                return cause;
            }
        }
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