protected final RetryRuleWithContent<O> retryRuleWithContent() {
        checkState(retryConfig != null, "No retryRuleWithContent set. Are you using RetryConfigMapping?");
        final RetryRuleWithContent<O> retryRuleWithContent = retryConfig.retryRuleWithContent();
        checkState(retryRuleWithContent != null, "retryRuleWithContent is not set.");
        return retryRuleWithContent;
    }
Returns the {@link RetryRuleWithContent}.

@throws IllegalStateException if the {@link RetryRuleWithContent} is not set
core/src/main/java/com/linecorp/armeria/client/retry/AbstractRetryingClient.java