エラー：HTTPステータス 500 - java.lang.NullPointerException

サーブレット、JSPの画面遷移でエラーが発生します。
HTTPステータス 500 - java.lang.NullPointerException

※質問登録画面でデータを入力し、質問一覧画面に遷移する際に
エラー発生します

不備、修正箇所等教えていただけたら幸いです。

java
1package servlet;
2
3import java.io.IOException;
4import java.util.List;
5
6import javax.servlet.RequestDispatcher;
7import javax.servlet.ServletException;
8import javax.servlet.annotation.WebServlet;
9import javax.servlet.http.HttpServlet;
10import javax.servlet.http.HttpServletRequest;
11import javax.servlet.http.HttpServletResponse;
12import javax.servlet.http.HttpSession;
13
14import model.GetQuestionListLogic;
15import model.PostQuestionLogic;
16import model.Question;
17/**
18 * Servlet implementation class Doctest
19 */
20
21@WebServlet("/RegistQuestionServlet")
22public class RegistQuestionServlet extends HttpServlet {
23 private static final long serialVersionUID = 1L;
24
25/**
26* @see HttpServlet#doget(HttpServletRequest request, HttpServletResponse response)
27*/
28protected void doGet(HttpServletRequest request, HttpServletResponse response)
29throws ServletException, IOException {
30//フォワード
31RequestDispatcher dispatcher =
32 request.getRequestDispatcher("/WEB-INF/jsp/QandARegist.jsp");
33 dispatcher.forward(request, response);
34}
35
36/**
37* @see HttpServlet#dopost(HttpServletRequest request, HttpServletResponse response)
38*/
39protected void doPost(HttpServletRequest request, HttpServletResponse response)
40throws ServletException, IOException {
41//文字コードエンコーディング
42request.setCharacterEncoding("UTF-8");
43//リクエストパラメータ取得
44// int id = request.getParameter("id");
45 String handle_name = request.getParameter("handle_name");
46 String title = request.getParameter("title");
47 String contents = request.getParameter("contents");
48 int urgency = Integer.parseInt(request.getParameter("urgency"));
49 String edit_delete_key = request.getParameter("edit_delete_key");
50 String regist_timestamp = request.getParameter("regist_timestamp");
51 String update_timestamp = request.getParameter("update_timestamp");
52
53// 質問リストに質問を追加
54 Question question = new Question(handle_name, title, contents, urgency, edit_delete_key, regist_timestamp, update_timestamp);
55 PostQuestionLogic postQuestionLogic = new PostQuestionLogic();
56 postQuestionLogic.execute(question);
57
58//質問リスト取得
59GetQuestionListLogic getQuestionListLogic = new GetQuestionListLogic();
60List<Question> questionList = getQuestionListLogic.execute();
61
62//セッションスコープにbeansのquestionを保存
63HttpSession session = request.getSession();
64session.setAttribute("handle_name", handle_name);
65session.setAttribute("title", title);
66session.setAttribute("contents", contents);
67session.setAttribute("urgency", urgency);
68session.setAttribute("edit_delete_key", edit_delete_key);
69session.setAttribute("regist_timestamp", regist_timestamp);
70session.setAttribute("update_timestamp", update_timestamp);
71
72//フォワード
73RequestDispatcher dispatcher =request.getRequestDispatcher("/WEB-INF/jsp/QandAList.jsp");
74dispatcher.forward(request, response);
75 }
76}
77

jsp
1<!-- QandAList.jsp(質問一覧画面) -->
2<%@ page language="java" contentType="text/html; charset=UTF-8"
3   pageEncoding="UTF-8" %>
4<%@ page import="model.Question"%>
5<%
6Question q = (Question)session.getAttribute("Question");
7%>
8
9<!DOCTYPE html>
10<html lang="ja">
11<head>
12  <meta charset="utf-8">
13  <meta name="viewport" content=“width=device-width,initial-scale=1.0”>
14  <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
15  <title>課題1</title>
16  <link rel="stylesheet" href="css/QandAList.css">
17</head>
18<body>
19<header>
20  <div class="container">
21    <p>質問一覧</p>
22    <a href="/QandASystem/RegistQuestionServlet">質問する</a>
23  </div>
24</header>
25<div class="main">
26  <div class="container">
27      <table border="1">
28        <thead>
29          <tr>
30            <th class="no" width="7%">No</th>
31            <th width="15%">緊急度</th>
32            <th width="40%">タイトル</th>
33            <th>登録者</th>
34            <th>登録日</th>
35            <th>更新日</th>
36          </tr>
37        </thead>
38        <tbody>
39          <tr>
40            <td>5</td>
41            <td><%=q.getUrgency()%></td>
42            <td><%=q.getTitle()%></td>
43            <td><%=q.getHandle_name() %></td>
44            <td><%=q.getRegist_timestamp() %></td>
45            <td><%=q.getUpdate_timestamp() %></td>
46          </tr>
47          <tr>
48            <td>4</td>
49            <td><%=q.getUrgency()%></td>
50            <td><%=q.getTitle()%></td>
51            <td><%=q.getHandle_name() %></td>
52            <td><%=q.getRegist_timestamp() %></td>
53            <td><%=q.getUpdate_timestamp() %></td>
54          </tr>
55          <tr>
56            <td>3</td>
57            <td><%=q.getUrgency()%></td>
58            <td><%=q.getTitle()%></td>
59            <td><%=q.getHandle_name() %></td>
60            <td><%=q.getRegist_timestamp() %></td>
61            <td><%=q.getUpdate_timestamp() %></td>
62          </tr>
63          <tr>
64            <td>2</td>
65            <td><%=q.getUrgency()%></td>
66            <td><%=q.getTitle()%></td>
67            <td><%=q.getHandle_name() %></td>
68            <td><%=q.getRegist_timestamp() %></td>
69            <td><%=q.getUpdate_timestamp() %></td>
70          </tr>
71          <tr>
72            <td>1</td>
73            <td><%=q.getUrgency()%></td>
74            <td><%=q.getTitle()%></td>
75            <td><%=q.getHandle_name() %></td>
76            <td><%=q.getRegist_timestamp() %></td>
77            <td><%=q.getUpdate_timestamp() %></td>
78          </tr>
79        </tbody>
80      </table>
81  </div>
82</div>
83<script src="js/main.js"></script>
84</body>
85</html>

jsp
1<!-- QandARegist.jsp(質問登録画面) -->
2<%@ page language="java" contentType="text/html; charset=UTF-8"
3   pageEncoding="UTF-8" %>
4
5<!DOCTYPE html>
6<html lang="ja">
7<head>
8  <meta charset="utf-8">
9  <title>質問登録画面</title>
10  <link rel="stylesheet" href="css/QandARegist.css">
11</head>
12<body>
13  <header>
14    <div class="container">
15      <div class="header-flex">
16        <div class="header-left">
17          <h3>質問登録</h3>
18        </div>
19        <div class="header-right">
20          <a href="/QandASystem/QuestionListServlet class="btn">戻る</a>
21        </div>
22     </div>
23    </div>
24  </header>
25  <section class="question-form">
26   <div class="container">
27   <form action="/QandASystem/RegistQuestionServlet" method="post">
28    <table border="1">
29      <tr>
30        <th>名前(ハンドルネーム)</th>
31        <td><input type="text" class="inp"></td>
32      </tr>
33      <tr>
34        <th>タイトル</th>
35        <td><input type="text" class="inp"></td>
36      </tr>
37      <tr>
38        <th class="contents">内容</th>
39        <td><textarea rows="16"></textarea></td>
40      </tr>
41      <tr class="urgency">
42        <th>緊急度</th>
43        <td>
44          <label><input type="radio" name="urgency" value="1">急いでいます</label>
45          <label><input type="radio" name="urgency" value="2">困ってます</label>
46          <label><input type="radio" name="urgency" value="3">いつでも</label>
47        </td>
48      </tr>
49      <tr>
50        <th>編集・削除キー</th>
51        <td><input type="text" class="inp"></td>
52      </tr>
53    </table>
54    <input type="submit" value="登録">
55    </form>
56   </div>
57  </section>
58</body>
59</html>