public static CancelledSubscriptionException get() {
        return Flags.verboseExceptionSampler().isSampled(CancelledSubscriptionException.class) ?
               new CancelledSubscriptionException() : INSTANCE;
    }
Returns a {@link CancelledSubscriptionException} which may be a singleton or a new instance, depending
on {@link Flags#verboseExceptionSampler()}'s decision.
core/src/main/java/com/linecorp/armeria/common/stream/CancelledSubscriptionException.java