访问时出现了错误，跳出了这段代码怎么回事。在别的电脑能够跳转！！！谢谢大佬们

Type Exception ReportMessage An exception occurred processing JSP page [/viewStudent.jsp] at line [17]Description The server encountered an unexpected condition that prevented it from fulfilling the request.Exception
org.apache.jasper.JasperException: An exception occurred processing JSP page [/viewStudent.jsp] at line [17]14: </tr>
15: 
16: <%
17: List<Student> students=studentUtil.getAllStudent();
18: Iterator<Student> it=students.iterator();
19: while(it.hasNext()) {
20:     Student temp=it.next();
Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:584)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:481)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:385)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:329)
javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
Root Cause
java.lang.NullPointerException
edu.gcp.dao.StudentDAOImpl.getAllStudent(StudentDAOImpl.java:20)
org.apache.jsp.viewStudent_jsp._jspService(viewStudent_jsp.java:136)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:443)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:385)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:329)
javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
Note The full stack trace of the root cause is available in the server logs.