NullPointerException ao enviar o arquivo.

Pessoal, estou recebendo uma nullpointerexception conforme abaixo.

GRAVE: Servlet.service() for servlet [dispatcher] in context with path [/casadocodigo] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause
java.lang.NullPointerException
    at br.com.casadocodigo.loja.infra.FileSaver.write(FileSaver.java:23)
    at br.com.casadocodigo.loja.controllers.ProdutoController.gravar(ProdutoController.java:54)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:215)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:781)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:721)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:83)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:943)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:877)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:863)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:648)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:212)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1096)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:674)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1500)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1456)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:745)

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ taglib uri="http://www.springframework.org/tags/form" prefix="form" %>
<%@ taglib uri="http://www.springframework.org/tags" prefix="s" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Livros de Java, Android, iPhone, Ruby, PHP e muito mais - Casa do Codigo</title>
</head>
<body>
    <form:form action="${s:mvcUrl('PC#gravar').build()}" method="post" commandName="produto" enctype="multipart/form-data">
        <div>
            <label>Título</label>
            <form:input path="titulo" />
            <form:errors path="titulo" />
        </div>

        <div>
            <label>Descrição</label>
            <form:textarea path="descricao" cols="30" rows="10" /> 
            <form:errors path="descricao" />
        </div>

        <div>
            <label>Data de Lançamento</label>
            <form:input path="dataLancamento" />
            <form:errors path="dataLancamento" />
        </div>

        <div>
            <label>Páginas</label>
            <form:input path="paginas" />
            <form:errors path="paginas" />
        </div>

        <c:forEach items="${tipos}" var="tipoPreco" varStatus="status">
            <div>
                <label>${tipoPreco}</label>
                <form:input path="precos[${status.index}].valor" />
                <form:hidden path="precos[${status.index}].tipo" value="${tipoPreco}" />
            </div>
        </c:forEach>
        <div>
            <label>Sumário</label>
            <input type="file" name="sumario">
        </div>
        <button type="submit">Cadastrar</button>
    </form:form>
</body>
</html>

    package br.com.casadocodigo.loja.controllers;

import java.util.List;

import javax.validation.Valid;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.validation.BindingResult;
import org.springframework.web.bind.WebDataBinder;
import org.springframework.web.bind.annotation.InitBinder;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.multipart.MultipartFile;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.support.RedirectAttributes;

import br.com.casadocodigo.loja.daos.ProdutoDAO;
import br.com.casadocodigo.loja.infra.FileSaver;
import br.com.casadocodigo.loja.models.Produto;
import br.com.casadocodigo.loja.models.TipoPreco;
import br.com.casadocodigo.loja.validacoes.ProdutoValidation;

@Controller
@RequestMapping("/produtos")
public class ProdutoController {

    @Autowired
    private ProdutoDAO dao;

    @Autowired
    private FileSaver fileSaver;

    @InitBinder
    public void initBinder(WebDataBinder binder){
        binder.addValidators(new ProdutoValidation());
    }

    @RequestMapping("/form")
    public ModelAndView form(Produto produto){
        ModelAndView modelAndView = new ModelAndView("produtos/form");
        modelAndView.addObject("tipos", TipoPreco.values());

        return modelAndView;
    }

    @RequestMapping(method=RequestMethod.POST)
    public ModelAndView gravar(MultipartFile file, @Valid Produto produto, BindingResult result, RedirectAttributes attributes){

        if(result.hasErrors()){    
            return form(produto);
        }

        String path = fileSaver.write("arquivos-sumario", file);

        produto.setSumarioPath(path);

        dao.gravar(produto);
        attributes.addFlashAttribute("sucesso", "Produto cadastrado com sucesso!");
        return new ModelAndView("redirect:produtos");
    }

    @RequestMapping(method=RequestMethod.GET)
    public ModelAndView listar(){
        List<Produto> produtos = dao.listar();
        ModelAndView modelAndView = new ModelAndView("produtos/lista");
        modelAndView.addObject("produtos", produtos);

        return modelAndView;
    }
}

package br.com.casadocodigo.loja.infra;

import java.io.File;
import java.io.IOException;

import javax.servlet.http.HttpServletRequest;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import org.springframework.web.multipart.MultipartFile;

@Component
public class FileSaver {

    @Autowired
    HttpServletRequest request;

    public String write(String baseFolder, MultipartFile file) {

        try {
            String realPath = request.getServletContext().getRealPath("/" + baseFolder);
            System.out.println(realPath);
            String path = realPath + "/" + file.getOriginalFilename();
            file.transferTo(new File(path));

            return baseFolder + "/" + file.getOriginalFilename();
        } catch (IllegalStateException | IOException e) {
            throw new RuntimeException(e);
        }

    }

}

package br.com.casadocodigo.loja.models;

import java.util.Calendar;
import java.util.List;

import javax.persistence.ElementCollection;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

import org.springframework.format.annotation.DateTimeFormat;

@Entity
public class Produto {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;
    private String titulo;
    private String descricao;
    private int paginas;

    @DateTimeFormat
    private Calendar dataLancamento;

    @ElementCollection
    private List<Preco> precos;

    private String sumarioPath;

    public String getTitulo() {
        return titulo;
    }

    public void setTitulo(String titulo) {
        this.titulo = titulo;
    }

    public String getDescricao() {
        return descricao;
    }

    public void setDescricao(String descricao) {
        this.descricao = descricao;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public int getPaginas() {
        return paginas;
    }

    public void setPaginas(int paginas) {
        this.paginas = paginas;
    }

    public Calendar getDataLancamento() {
        return dataLancamento;
    }

    public void setDataLancamento(Calendar dataLancamento) {
        this.dataLancamento = dataLancamento;
    }

    public List<Preco> getPrecos() {
        return precos;
    }

    public void setPrecos(List<Preco> precos) {
        this.precos = precos;
    }

    public String getSumarioPath() {
        return sumarioPath;
    }

    public void setSumarioPath(String sumarioPath) {
        this.sumarioPath = sumarioPath;
    }

    @Override
    public String toString() {
        return "Produto [titulo=" + titulo + ", descricao=" + descricao + ", paginas=" + paginas + "]";
    }

}