private void doRequest(long n) {
        final Subscription upstreamSubscription = this.upstreamSubscription;
        if (upstreamSubscription != null) {
            upstreamSubscription.request(n);
        } else {
            pendingDemand = LongMath.saturatedAdd(pendingDemand, n);
        }
    }
Closes the deferred stream without setting a delegate.

@throws IllegalStateException if the delegate has been set already or
                              if {@link #close()} or {@link #close(Throwable)} was called already.
core/src/main/java/com/linecorp/armeria/common/stream/DeferredStreamMessage.java