Add missed NullMarked to the xml.router package

* Fix NullAway for the `xPathExpression.evaluateAsString()` call in the `XPathRouter`

Author: artembilan

spring-integration-xml/src/main/java/org/springframework/integration/xml/router/XPathRouter.java

@@ -20,6 +20,7 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Objects;
 
 import org.jspecify.annotations.Nullable;
 import org.w3c.dom.DOMException;
@@ -42,9 +43,9 @@
  */
 public class XPathRouter extends AbstractMappingMessageRouter {
 
-	private final XPathExpression xPathExpression;
+	private final NodeMapper<Object> nodeMapper = new TextContentNodeMapper();
 
-	private NodeMapper<Object> nodeMapper = new TextContentNodeMapper();
+	private final XPathExpression xPathExpression;
 
 	private XmlPayloadConverter converter = new DefaultXmlPayloadConverter();
 
@@ -116,7 +117,7 @@ public String getComponentType() {
 	protected List<Object> getChannelKeys(Message<?> message) {
 		Node node = this.converter.convertToNode(message.getPayload());
 		if (this.evaluateAsString) {
-			return Collections.singletonList(this.xPathExpression.evaluateAsString(node));
+			return Collections.singletonList(Objects.requireNonNull(this.xPathExpression.evaluateAsString(node)));
 		}
 		else {
 			return this.xPathExpression.evaluate(node, this.nodeMapper);

spring-integration-xml/src/main/java/org/springframework/integration/xml/router/package-info.java

@@ -1,4 +1,5 @@
 /**
  * Provides XML message routers.
  */
+@org.jspecify.annotations.NullMarked
 package org.springframework.integration.xml.router;