private static void validateGreaterThanOrEqual(Duration larger, String largerFieldName,
                                           Duration smaller, String smallerFieldName) {
        if (larger.compareTo(smaller) < 0) {
            throw new IllegalArgumentException(largerFieldName + " must be greater than or equal to " +
                                               smallerFieldName);
        }
    }
Sets the function that returns an {@link Throwable} to terminate a pending request when the server is
shutting down. If unspecified, the request will be terminated with {@link ShuttingDownException} that
will be converted to an {@link HttpStatus#SERVICE_UNAVAILABLE} response.
core/src/main/java/com/linecorp/armeria/server/GracefulShutdownBuilder.java