Erro ao tentar cadastrar

package ConexaoBD;   
  
import java.sql.*;      
  
public class Conexao {      
  
   public static Connection con;      
   public static Statement stm;      
   public static ResultSet rs;      
   private static String res = "";      
  
   public static void conexao() {    
  
      try {      
  
         Class.forName("com.mysql.jdbc.Driver");      
         con = DriverManager.getConnection("jdbc:mysql://localhost/portal?zeroDateTimeBehavior=convertToNull","portal","alltec");      
         stm = con.createStatement();       
         res = "Conexão efetuada com sucesso";      
      } catch (Exception e) {      
         res = "não foi possível conectar ao banco" + e.getMessage();      
      }   
   }      
}

package Servlets;   
  
import java.io.IOException;   
import java.io.PrintWriter;   
import java.sql.Connection;   
import java.sql.SQLException;   
import javax.servlet.ServletException;   
import javax.servlet.http.HttpServlet;   
import javax.servlet.http.HttpServletRequest;   
import javax.servlet.http.HttpServletResponse;   
import ConexaoBD.Conexao;   
import Data.Data;   
  
  
public class CqaCadastraAlteraExclui extends HttpServlet {   
  
   protected void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException, SQLException {   
  
      response.setContentType("text/html;charset=ISO-8859-1");   
  
      PrintWriter out = response.getWriter();   
  
      String nomeSession = null;   
      String acao = null;   
  
      nomeSession = (String) request.getParameter("nomeSession");   
      acao = (String) request.getParameter("acao");   
  
      if (acao.equals("cadastra") || acao.equals("alterar") || acao.equals("excluir") || acao.equals("consultar") || acao.equals("alterar")) {   
         new Conexao();   
         String dt = Data.data_hora();               
      }   
      if (acao.equals("cadastra")) {   
  
         Conexao.stm.executeUpdate("insert into cqa (criador) values('"+nomeSession+"')");   
         Conexao.con.close();   
         response.sendRedirect("cqa/cqaDefineFluxo.jsp?cadastro=OK&criadorCqa="+nomeSession+"");   
      }   
   }   
   protected void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {   
      try {   
         processRequest(request, response);   
      } catch (SQLException e) {   
         e.printStackTrace();   
      }   
   }   
   protected void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {   
      try {   
         processRequest(request, response);   
      } catch (SQLException e) {   
         e.printStackTrace();   
      }   
   }   
}

type Exception report   
  
message    
  
description The server encountered an internal error () that prevented it from fulfilling this request.   
  
exception    
  
java.lang.NullPointerException   
   Servlets.CqaCadastraAlteraExclui.processRequest(CqaCadastraAlteraExclui.java:35)   
   Servlets.CqaCadastraAlteraExclui.doGet(CqaCadastraAlteraExclui.java:42)   
   javax.servlet.http.HttpServlet.service(HttpServlet.java:617)   
   javax.servlet.http.HttpServlet.service(HttpServlet.java:717)   
  
  
note The full stack trace of the root cause is available in the Apache Tomcat/6.0.20 logs.  
type Exception report