public boolean requiresResponseTrailers() {
        if (needsContentInRule()) {
            final RetryRuleWithContent<T> rule = retryRuleWithContent();
            assert rule != null;
            return rule.requiresResponseTrailers();
        } else {
            final RetryRule rule = retryRule();
            assert rule != null;
            return rule.requiresResponseTrailers();
        }
    }
Returns whether the associated {@link RetryRule} or {@link RetryRuleWithContent} requires
response trailers.
core/src/main/java/com/linecorp/armeria/client/retry/RetryConfig.java