Handle null from JDK HttpResponse#body

Closes gh-35692

Author: rstoyanchev

spring-web/src/main/java/org/springframework/http/client/reactive/JdkClientHttpResponse.java

@@ -98,7 +98,13 @@ private static ResponseCookie toResponseCookie(HttpCookie cookie, @Nullable Stri
 	}
 
 	private static Flux<DataBuffer> adaptBody(HttpResponse<Flow.Publisher<List<ByteBuffer>>> response, DataBufferFactory bufferFactory) {
-		return JdkFlowAdapter.flowPublisherToFlux(response.body())
+
+		Flow.Publisher<List<ByteBuffer>> body = response.body();
+		if (body == null) {
+			return Flux.empty();
+		}
+
+		return JdkFlowAdapter.flowPublisherToFlux(body)
 				.flatMapIterable(Function.identity())
 				.map(bufferFactory::wrap)
 				.doOnDiscard(DataBuffer.class, DataBufferUtils::release)