fix xml null bug

hutool-core/src/test/java/cn/hutool/core/util/XmlUtilTest.java

@@ -1,6 +1,7 @@
 package cn.hutool.core.util;
 
 import cn.hutool.core.collection.CollUtil;
+import cn.hutool.core.io.resource.ResourceUtil;
 import cn.hutool.core.map.MapBuilder;
 import cn.hutool.core.map.MapUtil;
 import org.junit.Assert;
@@ -64,6 +65,14 @@ public class XmlUtilTest {
 		Assert.assertEquals("ok", value);
 	}
 
+	@Test
+	public void xpathTest2() {
+		String result = ResourceUtil.readUtf8Str("test.xml");
+		Document docResult = XmlUtil.parseXml(result);
+		Object value = XmlUtil.getByXPath("//returnsms/message", docResult, XPathConstants.STRING);
+		Assert.assertEquals("ok", value);
+	}
+
 	@Test
 	public void xmlToMapTest() {
 		String xml = "<?xml version=\"1.0\" encoding=\"utf-8\" ?>"//

hutool-core/src/test/resources/test.xml

@@ -1,4 +1,8 @@
 <?xml version="1.0" encoding="utf-8" standalone="no"?>
+<!-- returnstatus 状态
+	 message 消息
+-->
+
 <returnsms>
 <returnstatus>Success（成功）</returnstatus>
 <message>ok</message>