请帮忙看下这错误

type Exception reportmessage description The server encountered an internal error () that prevented it from fulfilling this request.exception org.apache.jasper.JasperException: An exception occurred processing JSP page /news/showSecondTitle.jsp at line 1916: </tr>
17:      <% 
18:       String strParentId=request.getParameter("parentId");
19:      int parentID = Integer.parseInt(strParentId);
20:      List list2 = new SecondLevelTitleDboperation().getSecondTitle(parentID);
21:     
22:     %>
Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:524)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:435)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
root cause java.lang.NumberFormatException: null
java.lang.Integer.parseInt(Unknown Source)
java.lang.Integer.parseInt(Unknown Source)
org.apache.jsp.news.newSpare_jsp._jspService(newSpare_jsp.java:155)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:393)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
note The full stack trace of the root cause is available in the Apache Tomcat/6.0.14 logs.
左边显示一级标题的showFirstTitle.jsp
<% request.setCharacterEncoding("GBK");
String titleName=request.getParameter("titleName");
FirstLevelTitle firstLevelTitle = new FirstLevelTitle();
firstLevelTitle.setTitleName(titleName);
firstLevelTitle.setCreator("accp");FirstLevelTitleDboperation firstLevelTitleDboperation = new FirstLevelTitleDboperation();
int result=firstLevelTitleDboperation.insetOneRecord(firstLevelTitle);if(result > 0){
request.getRequestDispatcher("sucess.jsp").forward(request,response);
}else{
request.getRequestDispatcher("error.jsp").forward(request,response);
} %>
右边显示二级标题的showSecondTitle.jsp<% 
      String strParentId=request.getParameter("parentId");
     int parentID = Integer.parseInt(strParentId);
     List list2 = new SecondLevelTitleDboperation().getSecondTitle(parentID);
    
    %>
     <tr>
     <td valign="top" height="531"><br>
     <% 
     for(int i=0;i<list2.size();i++){
     SecondLevelTitle secondLevelTitle =(SecondLevelTitle)list2.get(i);
     %>
     <li>
     <a href="<%=secondLevelTitle.getFilePath()%>" target="_blank">
     <%=secondLevelTitle.getTitleName()%></a>
     </li>
     <br><br>
     <% 
     }
     %>前台：newSpare.jsp<tr>
    <td width="150" valign="top" align="left">
    <%@include file="showFirstTitle.jsp"%>
    </td>
    <td>
    <%@include file="showSecondTitle.jsp"%>
    </td>
    </tr>访问newSpare.jsp就出现上述错误，谢谢！