我的jsp程序运行时出现这样的错误，请问怎么解决？
 type Exception report

message 

description The server encountered an internal error () that prevented it from fulfilling this request.

exception 

org.apache.jasper.JasperException
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:372)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
    com.bjsxt.shopping.util.filter.IPFilter.doFilter(IPFilter.java:31)


root cause 

java.lang.NullPointerException
    com.bjsxt.shopping.category.CategoryService.getCategories(CategoryService.java:102)
    org.apache.jsp.Index_jsp._jspService(Index_jsp.java:84)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:324)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
    com.bjsxt.shopping.util.filter.IPFilter.doFilter(IPFilter.java:31)


note The full stack trace of the root cause is available in the Apache Tomcat/5.0.28 logs.