java.lang.NumberFormatException: null

Estou tentando dar insert no banco através de um sistema online e retorna este erro

    /*
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    package dao;

import Connection.Conexao;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;
import model.Continentes;

public class ContinentesDao {

private Connection connection;

public ContinentesDao() {
    connection = Conexao.getConnection();
}

/*public void addContinente(Continentes continentes) {
    String            sqlString = "update continente set nome=?, populacao=?, tamanho=? where cd_continente=?";
    PreparedStatement stm       = null;
    try {
        PreparedStatement preparedStatement = connection
                .prepareStatement("insert into continente(nome, populacao,tamanho) values (?, ?, ?)");
        // Parameters start with 1
        stm.setString(1, continentes.getNomeCont());
        stm.setLong(2, continentes.getPopulacaoCont());
        stm.setLong(2, continentes.getTamanhoCont());
        stm.executeUpdate();
        stm.close();

    } catch (SQLException e) {
        e.printStackTrace();
    }
}*/

    public void create(Continentes continentes) {
    
    Connection con = Conexao.getConnection();
    
    PreparedStatement stmt = null;

    try {
        stmt = con.prepareStatement("INSERT INTO continente (nome,populacao,tamanho)VALUES(?,?,?)");
        stmt.setString(1, continentes.getNomeCont());
        stmt.setLong(2, continentes.getPopulacaoCont());
        stmt.setLong(3, continentes.getTamanhoCont());
        stmt.setInt(4, continentes.getCdCont());


        stmt.executeUpdate();

        //JOptionPane.showMessageDialog(null, "Salvo com sucesso!");
    } catch (SQLException ex) {
        System.out.println(ex);
    } finally {
        Conexao.closeConnection(con);
    }

}

public void deleteContinentes(int cdCont) {
    String            sqlString = "update continente set nome=?, populacao=?, tamanho=? where cd_continente=?";
    PreparedStatement stm       = null;
    
    try {
        stm = connection.prepareStatement("delete from continente where cd_continente=?");
        // Parameters start with 1
        stm.setInt(1, cdCont);
        stm.executeUpdate();
        stm.close();

    } catch (SQLException e) {
        e.printStackTrace();
    }
}


public void updateContinentes(Continentes continentes) {
    
    String            sqlString = "update continente set nome=?, populacao=?, tamanho=? where cd_continente=?";
    PreparedStatement stm       = null;
    
    try {

        stm.setString(1, continentes.getNomeCont());
        stm.setLong(2, continentes.getPopulacaoCont());
        stm.setLong(3, continentes.getTamanhoCont());
        stm.setInt(4, continentes.getCdCont());
        stm.executeUpdate();
        stm.close();

    } catch (SQLException e) {
        e.printStackTrace();
    }
}
 


public List<Continentes> getAllContinentes() {
    List<Continentes> listaContinentes = new ArrayList<Continentes>();
    try {
        Statement stmt = connection.createStatement();
        ResultSet rs = stmt.executeQuery("select * from continente");
        while (rs.next()) {
            Continentes continentes = new Continentes();  
            continentes.setCdCont(rs.getInt("cd_continente"));
            continentes.setNomeCont(rs.getString("nome"));
            continentes.setPopulacaoCont(rs.getLong("populacao"));
            continentes.setTamanhoCont(rs.getLong("tamanho"));
            listaContinentes.add(continentes);
            
        }
    } catch (SQLException e) {
        e.printStackTrace();
    }

    return listaContinentes;
}

public Continentes getContinentesByCd(int cdCont) {
    Continentes continentes = new Continentes();
    try {
        PreparedStatement preparedStatement = connection.prepareStatement("select * from continente where cd_continente=?");
        preparedStatement.setInt(1, cdCont);
        ResultSet rs = preparedStatement.executeQuery();

        if (rs.next()) {
            continentes.setCdCont(rs.getInt("cd_continente"));
            continentes.setNomeCont(rs.getString("nome"));
            continentes.setPopulacaoCont(rs.getLong("populacao"));
            continentes.setTamanhoCont(rs.getLong("tamanho"));
        }
    } catch (SQLException e) {
        e.printStackTrace();
    }

    return continentes;
}

}

package controller;

import dao.ContinentesDao;
import java.io.IOException;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

import javax.servlet.RequestDispatcher;
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 model.Continentes;

@WebServlet(name = “Continentes”, urlPatterns = {"/ContinentesController"})
public class ContinentesController extends HttpServlet {
private static final long serialVersionUID = 1L;
private static String INSERT_OR_EDIT = “/continentes.jsp”;
private static String LIST_CONT = “/telaAdmin.jsp”;
private ContinentesDao dao;

public ContinentesController() {
    super();
    dao = new ContinentesDao();
}

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    String forward="";
    String action = request.getParameter("action");

    if (action.equalsIgnoreCase("delete")){
        int cdCont = Integer.parseInt(request.getParameter("cdCont"));
        dao.deleteContinentes(cdCont);
        forward = LIST_CONT;
        request.setAttribute("continentes", dao.getAllContinentes()); 
        
    } else if (action.equalsIgnoreCase("edit")){
        forward = INSERT_OR_EDIT;
        int cdCont = Integer.parseInt(request.getParameter("cdCont"));
        Continentes continentes = dao.getContinentesByCd(cdCont);
        request.setAttribute("continentes", continentes);
        
    } else if (action.equalsIgnoreCase("listContinentes")){
        forward = LIST_CONT;
        request.setAttribute("continentes", dao.getAllContinentes());
        
    } else {
        forward = INSERT_OR_EDIT;
    }

    RequestDispatcher view = request.getRequestDispatcher(forward);
    view.forward(request, response);
}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    Continentes continentes = new Continentes();
    
    continentes.setNomeCont(request.getParameter("nomeCont"));
    continentes.setPopulacaoCont(Long.parseLong(request.getParameter("populacaoCont")));
    continentes.setTamanhoCont(Long.parseLong(request.getParameter("tamanhoCont")));
    
    
    String cdCont = request.getParameter("cdCont");
    
    if(cdCont == null || cdCont.isEmpty())
    {
        dao.create(continentes);
    }
    else
    {
        continentes.setCdCont(Integer.parseInt(cdCont));
        dao.updateContinentes(continentes);
    }
    
    RequestDispatcher view = request.getRequestDispatcher(LIST_CONT);
    request.setAttribute("continentes", dao.getAllContinentes());
    view.forward(request, response);
}

}

Dica: sempre passe o erro completo e destaque a linha que o causou.

Em alguma das suas chamadas a Integer.parseInt(), está tendo um parâmetro null. Verifique se o parâmetro não é null antes ou faça um catch para numberformatexception.