Novamente java.lang.NullPointerException

Código baixado do link: https://caelum-online-public.s3.amazonaws.com/1001-servlets-parte2/05/1001-servlet-parte2-aula5.zip

HTTP Status 500 – Internal Server Error

Type Exception Report

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

Exception

java.lang.NullPointerException
    br.com.alura.gerenciador.servlet.AutorizacaoFilter.doFilter(AutorizacaoFilter.java:32)
    br.com.alura.gerenciador.servlet.MonitoramentoFilter.doFilter(MonitoramentoFilter.java:28)
Note A pilha de erros completa da causa principal está disponível nos logs do servidor.

Apache Tomcat/9.0.27

package br.com.alura.gerenciador.servlet;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;


//@WebFilter("/entrada")
@SuppressWarnings("unused")
public class AutorizacaoFilter implements Filter {


    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain chain) throws IOException, ServletException {

        System.out.println("AutorizacaoFilter");

        HttpServletRequest request = (HttpServletRequest) servletRequest;
        HttpServletResponse response = (HttpServletResponse) servletResponse;

        String paramAcao = request.getParameter("acao");

        HttpSession sessao = request.getSession();
        boolean usuarioNaoEstaLogado = (sessao.getAttribute("usuarioLogado") == null);
        boolean ehUmaAcaoProtegida = !(paramAcao.equals("Login") || paramAcao.equals("LoginForm"));

        if(ehUmaAcaoProtegida && usuarioNaoEstaLogado) {
            response.sendRedirect("entrada?acao=LoginForm");
            return;
        }

        chain.doFilter(request, response);
    }


}

package br.com.alura.gerenciador.servlet;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;

//@WebFilter(urlPatterns="/entrada")
@SuppressWarnings("unused")
public class MonitoramentoFilter implements Filter {

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {

        System.out.println("MonitoramentoFilter");


        long antes = System.currentTimeMillis();

        String acao = request.getParameter("acao");

        //executa a acao
        chain.doFilter(request, response);

        long depois = System.currentTimeMillis();
        System.out.println("Tempo de execu��o da acao " + acao + " -> " + (depois - antes));

    }

}