@Override
    public Throwable fillInStackTrace() {
        if (Flags.verboseExceptionSampler().isSampled(getClass())) {
            super.fillInStackTrace();
        }
        return this;
    }
Returns the {@link CircuitBreaker} that has detected the failure.
core/src/main/java/com/linecorp/armeria/client/circuitbreaker/FailFastException.java