session variabel i form. er altid null

Lige meget hvad jeg gør giver input fra den form altid null i min Servlet hvad sker der, har chekket andre svar kan ikke se hvad der er galt

form
<FORM method="post" action="/SmallPivot/GemSvar">
<INPUT type="text" name="b" size="20">
<INPUT type="submit"
    name="send" value="send"></FORM>

servlet

import java.io.IOException;
import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
* @version     1.0
* @author
*/
public class GemSvar extends HttpServlet {
    java.sql.Connection con = null;
    /**
    * @see javax.servlet.http.HttpServlet#void (javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)
    */
    public void doGet(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException {
//        HttpSession ses = req.getSession(true);
//        System.out.println(ses.getAttribute("bruger_cpr"));
        super.doPost(req, resp);

    }

    /**
    * @see javax.servlet.http.HttpServlet#void (javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)
    */
    public void doPost(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException {

        HttpSession ses = req.getSession(true);
        String s = (String) ses.getAttribute("b");
        //altid null hvad sker der
        System.out.println(s);
       

    }

    /**
    * @see javax.servlet.GenericServlet#void ()
    */
    public void init() throws ServletException {

        super.init();

        try {
            Class.forName("org.gjt.mm.mysql.Driver");
        } catch (ClassNotFoundException e) {
            System.err.println(e.getMessage());
        }
        //java.sql.Connection con = null;
        try {
            con =
                java.sql.DriverManager.getConnection(
                    "jdbc:mysql://127.0.0.1:3306/pivot",
                    "admin",
                    "pivot");
        } catch (Exception e) {
            System.err.println(e.getMessage());
        }

    }
}