Não consigo atualizar meu Objeto usando Spring MVC | Alura

Já consigo recuperar meu objeto da minha tabela para meu formulário, hora que vou persistir estou com erro.

Segue meu codigo.

Controller

/**
     * Método que recuprra a Tarefa Selecionada
     * @param tarefa
     * @param model
     * @return
     */
    @RequestMapping("mostraTarefaSelecionada")
    public String mostraFormularioAtualizacao(Tarefa tarefa,Model model){
        try {
            Connection connection = new ConnectionFactory().getConnection();
            TarefaDAO dao = new TarefaDAO(connection);
            model.addAttribute("tarefa", dao.buscaPorId(tarefa.getId()));
            return "tarefa/mostra";
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    /**
     * Após recuperar, atualiza o Objeto
     * @param id
     * @param model
     */
    @RequestMapping("atualizarTarefaSelecionada")
    public String buscaTarefa(Tarefa tarefa){
        try {
            Connection connection = new ConnectionFactory().getConnection();
            TarefaDAO dao = new TarefaDAO(connection);
            dao.atualizarTarefa(tarefa);
            return "redirect:listarTarefas";
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

DAO

public void atualizarTarefa(Tarefa tarefa) {
        String sql = "UPDATE tarefas SET descricao = ?, finalizado = ?, data_finalizacao = ? WHERE id = ?";

        try {
            PreparedStatement prepareStatement = conn.prepareStatement(sql);
            prepareStatement.setString(1, tarefa.getDescricao());
            prepareStatement.setBoolean(2,tarefa.isFinalizado());
            prepareStatement.setDate(3, new Date(tarefa.getDataFinalizacao().getTimeInMillis()));
            prepareStatement.setLong(4, tarefa.getId());

            prepareStatement.execute();
            prepareStatement.close();
            conn.close();

        } catch (SQLException e) {
            throw new RuntimeException(e);
        }
    }

meu Fomulário

<h3>Alterar tarefa - ${tarefa.id}</h3>

    <form action="atualizarTarefaSelecionada" method="post"> 
        <input type="hidden" name="id" value="${tarefa.id}">

        Descrição:<br />
        <textarea rows="6" cols="18" name="descricao" >    ${tarefa.descricao} </textarea><br /> 

        Finalizado? <br/>
        <input type="checkbox" name="finalizado" value="true" ${tarefa.finalizado ? 'checked' : '' } /> <br />
        Data Finalizacao:
        <input type="text" name="dataFinalizacao" value="<fmt:formatDate value="${tarefa.dataFinalizacao.time}" pattern="dd/MM/yyyy" />" /> <br /> 
        <input type="submit" value="Enviar">
    </form>

Meu Erro

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is java.lang.RuntimeException: java.lang.NullPointerException
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:982)
    org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:872)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:661)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
Root Cause
java.lang.RuntimeException: java.lang.NullPointerException
    br.com.caelum.tarefas.controller.TarefasController.buscaTarefa(TarefasController.java:124)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    java.lang.reflect.Method.invoke(Unknown Source)
    org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:221)
    org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136)
    org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:114)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738)
    org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:963)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
    org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:872)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:661)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
Root Cause
java.lang.NullPointerException
    br.com.caelum.tarefas.model.TarefaDAO.atualizarTarefa(TarefaDAO.java:114)
    br.com.caelum.tarefas.controller.TarefasController.buscaTarefa(TarefasController.java:121)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    java.lang.reflect.Method.invoke(Unknown Source)
    org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:221)
    org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136)
    org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:114)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738)
    org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:963)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
    org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:872)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:661)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)

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