src/jdk.incubator.httpclient/share/classes/jdk/incubator/http/BufferingSubscriber.java

*** 78,88 ****
  
      private volatile int state;
  
      BufferingSubscriber(HttpResponse.BodySubscriber<T> downstreamSubscriber,
                          int bufferSize) {
!         this.downstreamSubscriber = downstreamSubscriber;
          this.bufferSize = bufferSize;
          synchronized (buffersLock) {
              internalBuffers = new ArrayList<>();
          }
          state = UNSUBSCRIBED;
--- 78,88 ----
  
      private volatile int state;
  
      BufferingSubscriber(HttpResponse.BodySubscriber<T> downstreamSubscriber,
                          int bufferSize) {
!         this.downstreamSubscriber = Objects.requireNonNull(downstreamSubscriber);
          this.bufferSize = bufferSize;
          synchronized (buffersLock) {
              internalBuffers = new ArrayList<>();
          }
          state = UNSUBSCRIBED;