private static void warnIfExceptionIsRaised(Object retryRule, @Nullable Throwable cause) {
        if (cause != null) {
            logger.warn("Unexpected exception is raised from {}.", retryRule, cause);
        }
    }
Creates a new instance that decorates the specified {@link HttpClient}.
core/src/main/java/com/linecorp/armeria/client/retry/RetryingClient.java