Nullability fixes for AtomicReference variables

Closes gh-35514
Signed-off-by: Manu Sridharan <msridhar@gmail.com>

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

@@ -135,7 +135,7 @@ final class OutputStreamPublisher<T> implements Flow.Publisher<T> {
 
 		private final AtomicLong requested = new AtomicLong();
 
-		private final AtomicReference<Object> parkedThread = new AtomicReference<>();
+		private final AtomicReference<@Nullable Object> parkedThread = new AtomicReference<>();
 
 		private volatile @Nullable Throwable error;
 

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

@@ -20,6 +20,7 @@ import java.io.IOException;
 import java.io.UncheckedIOException;
 import java.net.URI;
 import java.time.Duration;
+import java.util.Objects;
 import java.util.concurrent.Executor;
 import java.util.concurrent.atomic.AtomicReference;
 
@@ -131,13 +132,13 @@ final class ReactorClientHttpRequest extends AbstractStreamingClientHttpRequest
 			return Mono.empty();
 		}
 
-		AtomicReference<Executor> executorRef = new AtomicReference<>();
+		AtomicReference<@Nullable Executor> executorRef = new AtomicReference<>();
 
 		return outbound
 				.withConnection(connection -> executorRef.set(connection.channel().eventLoop()))
 				.send(FlowAdapters.toPublisher(new OutputStreamPublisher<>(
 						os -> body.writeTo(StreamUtils.nonClosing(os)), new ByteBufMapper(outbound),
-						executorRef.getAndSet(null), null)));
+						Objects.requireNonNull(executorRef.getAndSet(null)), null)));
 	}
 
 	static IOException convertException(RuntimeException ex) {

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

@@ -81,7 +81,7 @@ final class SubscriberInputStream<T> extends InputStream implements Flow.Subscri
 
 	private final Queue<T> queue;
 
-	private final AtomicReference<Object> parkedThread = new AtomicReference<>();
+	private final AtomicReference<@Nullable Object> parkedThread = new AtomicReference<>();
 
 	private final AtomicInteger workAmount = new AtomicInteger();