public static RequestCancellationException get() {
        return Flags.verboseExceptionSampler().isSampled(RequestCancellationException.class) ?
               new RequestCancellationException() : INSTANCE;
    }
Returns a singleton {@link RequestCancellationException} or newly-created exception depending on
the result of {@link Sampler#isSampled(Object)} of {@link Flags#verboseExceptionSampler()}.
core/src/main/java/com/linecorp/armeria/server/RequestCancellationException.java