Update code regarding null-safety semantics

See gh-30083

spring-webflux/src/main/java/org/springframework/web/reactive/result/condition/CompositeRequestCondition.java

@@ -21,6 +21,7 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
 
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.ObjectUtils;
 import org.springframework.web.server.ServerWebExchange;
@@ -142,6 +143,7 @@ public class CompositeRequestCondition extends AbstractRequestCondition<Composit
 	 * <p>An empty {@code CompositeRequestCondition} matches to all requests.
 	 */
 	@Override
+	@Nullable
 	public CompositeRequestCondition getMatchingCondition(ServerWebExchange exchange) {
 		if (isEmpty()) {
 			return this;

spring-webflux/src/main/java/org/springframework/web/reactive/result/condition/ConsumesRequestCondition.java

@@ -194,6 +194,7 @@ public final class ConsumesRequestCondition extends AbstractRequestCondition<Con
 	 * or {@code null} if no expressions match.
 	 */
 	@Override
+	@Nullable
 	public ConsumesRequestCondition getMatchingCondition(ServerWebExchange exchange) {
 		ServerHttpRequest request = exchange.getRequest();
 		if (CorsUtils.isPreFlightRequest(request)) {

spring-webflux/src/main/java/org/springframework/web/reactive/result/condition/ParamsRequestCondition.java

@@ -21,6 +21,7 @@ import java.util.Collections;
 import java.util.LinkedHashSet;
 import java.util.Set;
 
+import org.springframework.lang.Nullable;
 import org.springframework.util.ObjectUtils;
 import org.springframework.web.bind.annotation.RequestMapping;
 import org.springframework.web.server.ServerWebExchange;
@@ -104,6 +105,7 @@ public final class ParamsRequestCondition extends AbstractRequestCondition<Param
 	 * or {@code null} otherwise.
 	 */
 	@Override
+	@Nullable
 	public ParamsRequestCondition getMatchingCondition(ServerWebExchange exchange) {
 		for (ParamExpression expression : this.expressions) {
 			if (!expression.match(exchange)) {

spring-webflux/src/main/java/org/springframework/web/reactive/result/condition/RequestConditionHolder.java

@@ -99,6 +99,7 @@ public final class RequestConditionHolder extends AbstractRequestCondition<Reque
 	 * holder, return the same holder instance.
 	 */
 	@Override
+	@Nullable
 	public RequestConditionHolder getMatchingCondition(ServerWebExchange exchange) {
 		if (this.condition == null) {
 			return this;