为什么我的JPA更新(编辑)选项不起作用

我正试图用JPA创建一个CRUD。插入新记录和删除记录都工作。但一旦我去更新，也就是ctrl.edit(cats(行，它就会返回错误：org.apache.jaster.JasperException:java.lang.NullPointerException

有人能检查一下我的代码并告知我是否遗漏了什么吗？我已经用JPA创建了实体和控制器。

<%@page contentType="text/html" pageEncoding="UTF-8"%>
<%@page import="entities.Categories"%>
<%@page import="controller.CategoriesJpaController"%>
<%@page import="java.util.List"%>
<!DOCTYPE html>
<html>
<head>
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.5.2/css/bootstrap.min.css" integrity="sha384-JcKb8q3iqJ61gNV9KGb8thSsNjpSL0n8PARn9HuZOnIxN0hoP+VmmDGMN5t9UJ0Z" crossorigin="anonymous">
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.5.2/js/bootstrap.min.js" integrity="sha384-B4gt1jrGC7Jh4AgTPSdUtOBvfO8shuf57BaghqFfPlYxofvL8/KUEfYiJOMMV+rV" crossorigin="anonymous"></script>

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap.min.css">
<script src="https://code.jquery.com/jquery-1.12.4.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/js/bootstrap.min.js"></script>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>CATEGORIAS</title>

<script>
function cargar(id,nom,des)
{
document.modalito.txtcatid.value = id; 
document.modalito.txtcatname.value = nom; 
document.modalito.txtcatdes.value = des;
}
</script>

</head>
<body>
<%
HttpSession sesion = request.getSession(); 
//validar que solo si hay sesion activa pueda entrar
//la unica sesion es usuario y nivel
if(sesion.getAttribute("usuario")==null && sesion.getAttribute("nivel")==null)
{
response.sendRedirect("../login/index_login.jsp");
}

if(sesion.getAttribute("usuario")!=null && sesion.getAttribute("nivel")!=null)
{
String useruser = sesion.getAttribute("usuario").toString();
String nivel = sesion.getAttribute("nivel").toString();
%>

<nav class="navbar navbar-expand navbar-dark bg-dark static-top">

<hr>
<p style="color:white; font-size: 20px;"> Bienvenido <%=useruser%> (Nivel: <%=nivel%>) |         <a style="color:white;" href="${pageContext.request.contextPath}/index.jsp"> | Home | </a></p> 
<hr>

</nav>

<%
}
response.setHeader("Pragma","no-cache");
response.setHeader("Cache-Control", "no-cache, no-store, must-revalidate"); 
response.setDateHeader ("Expires", 0); 
%>

<br><br>
<h3 align="center">Formulario Categorias</h3>
<hr>

<button style="margin-left: 45%;" type="button" class="btn btn-primary btn-lg" data-toggle="modal" data-target="#miModal">
Ingresar Nuevo
</button>
<br><br>

<pre align="center">CONTENIDO DE LA TABLA PRODUCTOS</pre>
<br>

<%
List <Categories> ls; 
CategoriesJpaController ctrl = new CategoriesJpaController(); 
Categories cats = new Categories();
ls = ctrl.findCategoriesEntities(); 


if(request.getParameter("btnGuardar")!=null || request.getParameter("btnMod")!=null || request.getParameter("btnEliminar")!=null)
{
//guardar en un objeto producto lo del form
cats.setCategoryID(Integer.parseInt(request.getParameter("txtcatid")));
cats.setCategoryName(request.getParameter("txtcatname"));
cats.setDescription(request.getParameter("txtcatdes")); 
}



if(request.getParameter("btnGuardar")!=null)
{
ctrl.create(cats);
out.print("<script>alert('Exito al insertar');window.location.href = 'vCategoria.jsp';</script>");
ls=ctrl.findCategoriesEntities();
}
else if(request.getParameter("btnMod")!=null)
{                    
ctrl.edit(cats);
out.print("<script>alert('Exito al modificar');window.location.href = 'vCategoria.jsp';</script>");
ls=ctrl.findCategoriesEntities();
}
else if(request.getParameter("btnEliminar")!=null)
{                    
ctrl.destroy(cats.getCategoryID());
out.print("<script>alert('Exito al eliminar');window.location.href = 'vCategoria.jsp';</script>");
ls=ctrl.findCategoriesEntities();
}

%>

<div style="width: 700px; position: relative; margin-left: 27%;">
<table border="1" class="table">
<thead class="thead-dark">
<tr>
<th class="text-center">ID CATEGORIA</th>
<th class="text-center">NOMBRE CATEGORIA</th>
<th class="text-center">DESCRIPCIÓN</th>
</tr>
</thead>
<tbody>
<%
for(Categories c : ls)
{

%>
<tr>
<td class="text-center"><%= c.getCategoryID()%>
<a href="javascript:cargar('<%= c.getCategoryID() %>','<%= c.getCategoryName()%>','<%= c.getDescription() %>')">
<img src="../recursos/editar.jpg" width="25px" height="25px" data-toggle="modal" data-target="#miModal">
</a>
</td>
<td class="text-center"><%= c.getCategoryName() %></td>
<td class="text-center"><%= c.getDescription() %></td>
</tr>
<%
}
%>
</tbody>
</table>
</div>
</body>
<!--Este es el formulario modal-->
<div class="modal fade" id="miModal" tabindex="-1" role="dialog" aria-labelledby="myModalLabel" aria-hidden="true">
<div class="modal-dialog" role="document">
<div class="modal-content">
<div class="modal-header">

<h4 class="modal-title" id="myModalLabel">Formulario de Registro</h4>
<button type="button" class="close" data-dismiss="modal" aria-label="Close">
<span aria-hidden="true">&times;</span>
</button>
</div>
<div class="modal-body">
<div class="form-group">
<form action="vCategoria.jsp" method="POST" name="modalito">
<input type="text" name="txtcatid" placeholder="ID Categoria" class="form-control"  /><br>
<input type="text" name="txtcatname" placeholder="Nombre Categoria" class="form-control" /><br>
<input type="text" name="txtcatdes" placeholder="Descripción" class="form-control" /><br>


<input type="submit" name="btnGuardar" class="btn btn-primary" value="Guardar"/>
<input type="submit" name="btnMod" class="btn btn-info" value="Modificar"/>
<input type="submit" name="btnEliminar" class="btn btn-danger" value="Eliminar"/>
<input type="hidden" value="nuevo" name="opcion" /><br>
</form>
</div>
</div>
</div>
</div>
</div>
<!--Hasta aquí el modal-->

</body>

对不起，为了以Resolved的身份发布，我在这里找到了答案：es.stackoverflow.com/a/104830它是西班牙语的，但确实有帮助。

我只是在有问题的实体上启动了我的OneToMany列表，并解决了它。

@OneToMany(mappedBy = "categoryID") private List<Products> productsList = new 
ArrayList<Products>

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