How can i use a checkbox value in an if-statemnet? - java servlet

I want to insert something into my database based on a checkbox parameter that i get from a jsp file. I tried this and it does not work for some reason. I also printed the output of the checkbox value when it was checked and when it wasnt. When it wasnt i got "null" and when it was checked i got "on". I tried both "kurs == on" and "kurs != null" but none worked. What am i doing wrong?

my servlet:

package bacit.web.bacit_web;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import javax.servlet.*;
import java.sql.Date;

@WebServlet(name = "RegisterUserServlet", value = "/RegisterUserServlet")
public class RegisterUserServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        response.setContentType("text/html");
        PrintWriter out = response.getWriter();

        int userID = 4;
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        String fname = request.getParameter("fname");
        String lname = request.getParameter("lname");
        String phone = request.getParameter("phone");
        String kurs = request.getParameter("kurs");


        Connection db = null;
        try {
            db = DBUtils.getINSTANCE().getConnection(out);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }

        if (kurs != null) {
            String query1 = "insert into CERTIFICATE (USER_ID, COURSE_ID) values (?, 1)";
            try {
                PreparedStatement statement = db.prepareStatement(query1);

                statement.setInt(1, userID);
            }
            catch (SQLException e) {
                e.printStackTrace();
            }

            String query = "insert into USER (Fname, Lname, Phone, Username, Password) values (?, ?, ?, ?, ?)";
            try {
                PreparedStatement statement = db.prepareStatement(query);

                statement.setString(1, fname);
                statement.setString(2, lname);
                statement.setString(3, phone);
                statement.setString(4, username);
                statement.setString(5, password);

                ResultSet rs = statement.executeQuery();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        } else {
            String query = "insert into USER (Fname, Lname, Phone, Username, Password) values (?, ?, ?, ?, ?)";
            try {
                PreparedStatement statement = db.prepareStatement(query);

                statement.setString(1, fname);
                statement.setString(2, lname);
                statement.setString(3, phone);
                statement.setString(4, username);
                statement.setString(5, password);

                ResultSet rs = statement.executeQuery();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        out.println(kurs);
    }
}

and my jsp:

<div>
    <label for="kurs"> Personløftersertifikat </label>
    <input type="checkbox" name="kurs" id="kurs">
</div>