大家好，请你们帮我看看以下这个异常代码代表的是什么意思，应该怎么处理才能够解决呢。谢谢！
500 Servlet Exception
java.lang.NullPointerException
at MyBean.dbcon.executeQuery(dbcon.java:32)
at _topiclist__jsp._jspService(/topiclist.jsp:162)
at com.caucho.jsp.JavaPage.service(JavaPage.java:75)
at com.caucho.jsp.Page.subservice(Page.java:506)
at com.caucho.server.http.FilterChainPage.doFilter(FilterChainPage.java:182)
at com.caucho.server.http.Invocation.service(Invocation.java:315)
at com.caucho.server.http.CacheInvocation.service(CacheInvocation.java:135)
at com.caucho.server.http.HttpRequest.handleRequest(HttpRequest.java:253)
at com.caucho.server.http.HttpRequest.handleConnection(HttpRequest.java:171)
at com.caucho.server.TcpConnection.run(TcpConnection.java:139)
at java.lang.Thread.run(Thread.java:595)
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Resin 2.1.16 (built Tue Feb 15 11:12:27 PST 2005)
