Spring Boot提交含复选框与多文件的表单时触发MultipartException问题求助

大家好，我遇到了一个特别诡异的问题，想请各位帮忙分析排查一下：

我正在做Spring Boot + Thymeleaf的联系人添加功能，表单里包含了常规输入字段、文件上传项，还有一个「Mark as Favourite」的复选框。奇怪的是，不勾选这个复选框时，表单提交（包括文件上传）完全正常；但只要勾选它再提交，直接就弹出500错误，错误页面提示：

Whitelabel Error Page stating: There was an unexpected error (type=Internal Server Error, status=500). Failed to parse multipart servlet request org.springframework.web.multipart.MultipartException: Failed to parse multipart servlet request

我反复确认后发现，请求根本没到达我的控制器方法，是在Spring解析multipart请求的阶段就失败了。而且我已经排除了文件上传的问题——因为不勾选复选框时，不管传多大的文件（在配置范围内）都能正常提交，所以肯定不是文件大小或者格式的锅。

下面是我用到的完整HTML表单代码（代码末尾可能有点截断，是粘贴时的问题）：

<!doctype html>
<html lang="en" th:replace="~{base::parent(~{::#content}, ~{:: title}, ~{:: script})}">
<head>
<title th:text="${user.name + ' | Add Contacts'}">Add Contacts</title>
</head>
<body>
<div id="content" class="pl-64 pt-24">
<div th:replace="~{user/sidebar::sidebar}"></div>
<div class="pl-4 pr-4 md:pl-10">
<div class="grid grid-cols-1 md:grid-cols-12 gap-6">
<div class="md:col-span-3">
<div class="card block m-20 mt-0 p-6 bg-white border border-gray-200 rounded-lg shadow-sm hover:bg-gray-100 hover:shadow-md dark:bg-gray-800 dark:border-gray-700 dark:hover:bg-gray-700 transition-all duration-500 ease-in-out">
<div th:replace="~{message::messageBox}"></div>
<h1 class="text-2xl font-semibold text-gray-900 dark:text-white mb-4">Add New Contacts</h1>
<p class="text-gray-900 dark:text-gray-300 mb-10">Fill in the details below to add new contacts. </p>
<form th:action="@{/user/contacts/save}" method="post" th:object="${contactForm}" enctype="multipart/form-data" novalidate>
<div class="grid gap-6 mb-6 md:grid-cols-2">
<!-- Name -->
<div>
<label for="name" class="block mb-2 text-sm font-medium text-gray-900 dark:text-white">Full Name</label>
<input type="text" id="name" name="name" th:field="*{name}" class="bg-gray-50 border border-gray-300 text-gray-900 text-sm rounded-lg focus:ring-blue-500 focus:border-blue-500 block w-full p-2.5 dark:bg-gray-700 dark:border-gray-600 dark:placeholder-gray-400 dark:text-white dark:focus:ring-blue-500 dark:focus:border-blue-500" placeholder="Full Name" required/>
<p th:if="${#fields.hasErrors('name')}" th:errors="*{name}" class="text-red-500 text-sm font-medium mt-1"></p>
</div>
<!-- Email -->
<div>
<label for="email" class="block mb-2 text-sm font-medium text-gray-900 dark:text-white">Email address</label>
<input type="email" id="email" name="email" th:field="*{email}" class="bg-gray-50 border border-gray-300 text-gray-900 text-sm rounded-lg focus:ring-blue-500 focus:border-blue-500 block w-full p-2.5 dark:bg-gray-700 dark:border-gray-600 dark:placeholder-gray-400 dark:text-white dark:focus:ring-blue-500 dark:focus:border-blue-500" placeholder="name@company.com" required />
<p th:if="${#fields.hasErrors('email')}" th:errors="*{email}" class="text-red-500 text-sm font-medium mt-1"></p>
</div>
<!-- Phone -->
<div>
<label for="phoneNumber" class="block mb-2 text-sm font-medium text-gray-900 dark:text-white">Phone Number</label>
<input type="tel" id="phoneNumber" name="phoneNumber" th:field="*{phoneNumber}" class="bg-gray-50 border border-gray-300 text-gray-900 text-sm rounded-lg focus:ring-blue-500 focus:border-blue-500 block w-full p-2.5 dark:bg-gray-700 dark:border-gray-600 dark:placeholder-gray-400 dark:text-white dark:focus:ring-blue-500 dark:focus:border-blue-500" placeholder="XXXXXXXXXX" pattern="[0-9]{10}" required />
<p th:if="${#fields.hasErrors('phoneNumber')}" th:errors="*{phoneNumber}" class="text-red-500 text-sm font-medium mt-1"></p>
</div>
<!-- Address -->
<div>
<label for="address" class="block mb-2 text-sm font-medium text-gray-900 dark:text-white">Address</label>
<input type="text" id="address" name="address" th:field="*{address}" class="bg-gray-50 border border-gray-300 text-gray-900 text-sm rounded-lg focus:ring-blue-500 focus:border-blue-500 block w-full p-2.5 dark:bg-gray-700 dark:border-gray-600 dark:placeholder-gray-400 dark:text-w

我已经检查了spring.servlet.multipart相关的配置（比如max-file-size、max-request-size）都是合理值，而且不勾选复选框时所有功能都正常。现在实在搞不懂，一个简单的布尔值复选框，为什么会导致multipart请求解析失败？有没有人遇到过类似的问题，或者能给我一些排查方向？

内容来源于stack exchange