Review nullability declaration on XPathExpression and XPathOperations

Closes gh-1727

Author: snicoll

spring-xml/src/main/java/org/springframework/xml/xpath/JaxenXPathExpressionFactory.java

@@ -171,10 +171,10 @@ public List<Node> evaluateAsNodeList(Node node) {
 		}
 
 		@Override
-		public <T> List<T> evaluate(Node context, NodeMapper<T> nodeMapper) throws XPathException {
+		public <T> List<@Nullable T> evaluate(Node context, NodeMapper<T> nodeMapper) throws XPathException {
 			try {
 				List<?> nodes = this.xpath.selectNodes(context);
-				List<T> results = new ArrayList<>(nodes.size());
+				List<@Nullable T> results = new ArrayList<>(nodes.size());
 				for (int i = 0; i < nodes.size(); i++) {
 					Node node = (Node) nodes.get(i);
 					try {

spring-xml/src/main/java/org/springframework/xml/xpath/JaxenXPathTemplate.java

@@ -148,12 +148,13 @@ public String evaluateAsString(String expression, Source context) throws XPathEx
 	}
 
 	@Override
-	public <T> List<T> evaluate(String expression, Source context, NodeMapper<T> nodeMapper) throws XPathException {
+	public <T> List<@Nullable T> evaluate(String expression, Source context, NodeMapper<T> nodeMapper)
+			throws XPathException {
 		try {
 			XPath xpath = createXPath(expression);
 			Element element = getRootElement(context);
 			List<?> nodes = xpath.selectNodes(element);
-			List<T> results = new ArrayList<>(nodes.size());
+			List<@Nullable T> results = new ArrayList<>(nodes.size());
 			for (int i = 0; i < nodes.size(); i++) {
 				Node node = (Node) nodes.get(i);
 				try {

spring-xml/src/main/java/org/springframework/xml/xpath/Jaxp13XPathExpressionFactory.java

@@ -165,9 +165,9 @@ public Node evaluateAsNode(Node node) {
 		}
 
 		@Override
-		public <T> List<T> evaluate(Node node, NodeMapper<T> nodeMapper) throws XPathException {
+		public <T> List<@Nullable T> evaluate(Node node, NodeMapper<T> nodeMapper) throws XPathException {
 			NodeList nodes = (NodeList) evaluate(node, XPathConstants.NODESET);
-			List<T> results = new ArrayList<>(nodes.getLength());
+			List<@Nullable T> results = new ArrayList<>(nodes.getLength());
 			for (int i = 0; i < nodes.getLength(); i++) {
 				try {
 					results.add(nodeMapper.mapNode(nodes.item(i), i));

spring-xml/src/main/java/org/springframework/xml/xpath/Jaxp13XPathTemplate.java

@@ -123,9 +123,10 @@ public double evaluateAsDouble(String expression, Source context) throws XPathEx
 	}
 
 	@Override
-	public <T> List<T> evaluate(String expression, Source context, NodeMapper<T> nodeMapper) throws XPathException {
+	public <T> List<@Nullable T> evaluate(String expression, Source context, NodeMapper<T> nodeMapper)
+			throws XPathException {
 		NodeList nodes = (NodeList) evaluate(expression, context, XPathConstants.NODESET);
-		List<T> results = new ArrayList<>();
+		List<@Nullable T> results = new ArrayList<>();
 		if (nodes != null) {
 			for (int i = 0; i < nodes.getLength(); i++) {
 				try {

spring-xml/src/main/java/org/springframework/xml/xpath/XPathExpression.java

@@ -121,6 +121,6 @@ public interface XPathExpression {
 	 * @throws XPathException in case of XPath errors
 	 * @see <a href="http://www.w3.org/TR/xpath#node-sets">XPath specification</a>
 	 */
-	<T> List<T> evaluate(Node node, NodeMapper<T> nodeMapper) throws XPathException;
+	<T> List<@Nullable T> evaluate(Node node, NodeMapper<T> nodeMapper) throws XPathException;
 
 }

spring-xml/src/main/java/org/springframework/xml/xpath/XPathOperations.java

@@ -133,7 +133,7 @@ public interface XPathOperations {
 	 * @throws XPathException in case of XPath errors
 	 * @see <a href="http://www.w3.org/TR/xpath#node-sets">XPath specification</a>
 	 */
-	<T> List<T> evaluate(String expression, Source context, NodeMapper<T> nodeMapper) throws XPathException;
+	<T> List<@Nullable T> evaluate(String expression, Source context, NodeMapper<T> nodeMapper) throws XPathException;
 
 	/**
 	 * Evaluates the given expression, handling the result {@link Node} objects on a