final CircuitBreakerRuleWithContent<O> ruleWithContent() {
        checkState(ruleWithContent != null, "ruleWithContent is not set.");
        return ruleWithContent;
    }
Returns the {@link CircuitBreakerRuleWithContent}.

@throws IllegalStateException if the {@link CircuitBreakerRuleWithContent} is not set
core/src/main/java/com/linecorp/armeria/client/circuitbreaker/AbstractCircuitBreakerClient.java