RetryRuleWithContent<T> fromRetryRule() {
        requireNonNull(retryRule, "retryRule");
        if (fromRetryRule == null) {
            logger.warn(
                    "A RetryRuleWithContent is being generated from a RetryRule. " +
                    "You are probably using a RetryRule with a RetryingRpcClient. " +
                    "Please ensure that this is intentional.");
            fromRetryRule = RetryRuleUtil.fromRetryRule(retryRule);
        }
        return fromRetryRule;
    }
Returns the {@link RetryRule} converted from the {@link RetryRuleWithContent} of this config.
core/src/main/java/com/linecorp/armeria/client/retry/RetryConfig.java