事件处理器，断点跟踪到characters方法为什么程序不朝下跑了？

1.新建一个Student类，成员变量name,location,grade(为了方便，grade可以是String)
2.xml文件，exam.xml
<?xml version="1.0" encoding="UTF-8"?>
<exam>
    <student>
        <name>李四</name>
        <location>沈阳</location>
        <grade>59</grade>
    </student>
    <student>
        <name>的</name>
        <location>队伍</location>
        <grade>34343</grade>
    </student>
</exam>

3.问题代码
public class Xml封装对象返回List {

    @Test
    public void Test() throws Exception, SAXException {
        SAXParserFactory factory = SAXParserFactory.newInstance();
        SAXParser sp = factory.newSAXParser();
        XMLReader reader = sp.getXMLReader();
        MyHandle h = new MyHandle();
        reader.setContentHandler(h);
        reader.parse("src/exam.xml");
        List<Student> list = h.getList();
        System.out.println(list.get(1));
    }

    class MyHandle extends DefaultHandler {
        private List list = new ArrayList();// 解析到一本书就放在list集合里面
        private String currentTag;// 记住解析到的是什么标签
        private Student student;

        public List getList() {
            return list;
        }

        public void startElement(String uri, String localName, String name,
                Attributes attributes) throws SAXException {
            currentTag = name;
            if (currentTag.equals("student")) {
                student = new Student();
            }
        }

        public void characters(char[] ch, int start, int length)
                throws SAXException {
            if (currentTag.equals("name")) {
                String names = new String(ch, start, length);
                student.setNane(names);
            }
            if (currentTag.equals("location")) {
                String location = new String(ch, start, length);
                student.setLocation(location);
            }
            if (currentTag.equals("grade")) {
                String grade = new String(ch, start, length);
                student.setGrade(grade);
            }
        }

        public void endElement(String uri, String localName, String named)
                throws SAXException {
            if (named.equals("student")) {
                list.add(student);
            }
            currentTag = null;
        }
    }
}
----------------解决方案--------------------------------------------------------
错误是空指针异常，异常原因还是知道，但是不知道为什么跟踪到currentTag=null时，程序不跑了。
----------------解决方案--------------------------------------------------------