erro 500, mesmo problema do amigo abaixo | Java Servlet: programação web Java

estou com o mesmo problema do amigo abaixo, não consigo usar a minha lista de empresas no jsp, ela sempre devolme null

listaEmpresa.jsp:

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<%@ page import="java.util.List"%>
<%@ page import="java.util.ArrayList"%>
<%@page import="br.com.caelum.gerenciador.servlet.Empresa"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
    Lista de empresas: <br/>
    <ul>
    <%
        List<Empresa> lista = (List<Empresa>)request.getAttribute("empresas");
        for (Empresa empresa : lista) {
    %>
        <li><%= empresa.getNome() %></li>
    <%
        }
    %>
    </ul>
</body>
</html>

ListaEmpresaServlet:

package br.com.caelum.gerenciador.servlet;

import java.io.IOException;
import java.util.List;

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;

@WebServlet("/listaEmpresas")
public class ListaEmpresasServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

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

        Banco banco = new Banco();
        List<Empresa> lista = banco.getEmpresa();

        request.setAttribute("empresas", lista);

        RequestDispatcher rd = request.getRequestDispatcher("/listaEmpresa.jsp");

        rd.forward(request, response);        
    }
}

erro:

HTTP Status 500 – Internal Server Error
Type Exception Report

Message An exception occurred processing [/listaEmpresa.jsp] at line [17]

Description The server encountered an unexpected condition that prevented it from fulfilling the request.

Exception

org.apache.jasper.JasperException: An exception occurred processing [/listaEmpresa.jsp] at line [17]

14:     <ul>
15:     <%
16:         List<Empresa> lista = (List<Empresa>)request.getAttribute("empresas");
17:         for (Empresa empresa : lista) {
18:     %>
19:         <li><%= empresa.getNome() %></li>
20:     <%


Stacktrace:
    org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:610)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:499)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:379)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:327)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:764)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
Root Cause

java.lang.NullPointerException: Cannot invoke "java.util.List.iterator()" because "lista" is null
    org.apache.jsp.listaEmpresa_jsp._jspService(listaEmpresa_jsp.java:138)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:764)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:466)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:379)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:327)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:764)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
Note A pilha de erros completa da causa principal está disponível nos logs do servidor.