Spring Bootにて入力チェックをBean Validationを使って実装しようとしているが500エラーになってしまう。

Question

前提・実現したいこと

Spring Bootを用いてとあるサイトを作っております。
現在ユーザー登録画面を作成しており、Bean Validationを使って入力フォームのチェックをしようとしているのですが、
POSTを送信するとThymeleafのTemplateInputExceptionエラーが発生してしまい、うまく動作することができません。
デバッグを使いsubmitを送信した後の動きを1ステップずつ確認していきましたが、return の直後にエラーが出てしまうため、
HTML側の問題だとは思っていましたが、エラーのif文をコメントアウトしたら動いたので、どちらが原因なのかが分かりません。
どうかご教示をお願いします。

発生している問題・エラーメッセージ

There was an unexpected error (type=Internal Server Error, status=500).
Error resolving template [/account/register], template might not exist or might not be accessible by any of the configured Template Resolvers
org.thymeleaf.exceptions.TemplateInputException: Error resolving template [/account/register], template might not exist or might not be accessible by any of the configured Template Resolvers
	at org.thymeleaf.engine.TemplateManager.resolveTemplate(TemplateManager.java:869)
	at org.thymeleaf.engine.TemplateManager.parseAndProcess(TemplateManager.java:607)
	at org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1098)
	at org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1072)
	at org.thymeleaf.spring5.view.ThymeleafView.renderFragment(ThymeleafView.java:362)
	at org.thymeleaf.spring5.view.ThymeleafView.render(ThymeleafView.java:189)
	at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1373)
	at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1118)
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1057)
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943)
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)
	at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:909)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:660)
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:320)
	at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:126)
	at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:90)
	at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334)
	at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:118)
	at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334)
	at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:137)
	at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334)
	at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:111)
	at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334)
	at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:158)
	at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334)
	at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:63)
	at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334)
	at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:200)
	at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334)
	at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:116)
	at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334)
	at org.springframework.security.web.csrf.CsrfFilter.doFilterInternal(CsrfFilter.java:141)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
	at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334)
	at org.springframework.security.web.header.HeaderWriterFilter.doHeadersAfter(HeaderWriterFilter.java:92)
	at org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:77)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
	at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334)
	at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:105)
	at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334)
	at org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:56)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
	at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334)
	at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:215)
	at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:178)
	at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:358)
	at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:271)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)

    ~~~ org.apache 省略 ~~~

	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.base/java.lang.Thread.run(Thread.java:834)

該当のソースコード

//コントローラー
    @RequestMapping(value = "/account/register", method = RequestMethod.GET)
	public String goToRegister(Model model) {


		model.addAttribute("accountForm",new accountForm());


		return "accountRegister";
	}

	@RequestMapping(value = "/account/register", method = RequestMethod.POST)
	public String accountRegister(@Validated @ModelAttribute AccountForm accountForm ,BindingResult result,Model model) {

		if (result.hasErrors()) {
			List<String> errorList = new ArrayList<String>();

			for(ObjectError error : result.getAllErrors()) {
				errorList.add(error.getDefaultMessage());
			}

			model.addAttribute("accountForm",new AccountForm());
			model.addAttribute("validationError", errorList);
			return "accountRegister";
		}



		model.addAttribute("accountForm",accountForm); // 入力内容確認用

		return "accountRegister";
	}

@Data
@Getter
@Setter
public class OperationSystemForm implements Serializable{

	private static final long serialVersionUID = 1L;


	
	@NotBlank(message="IDを入力してください。")
	@Size(max=3,message="IDは3文字以内で入力してください。")
	private String name;


	@NotBlank(message="パスワードを入力してください。")
	@Size(max=3,message="パスワードは3文字以内で入力してください。")
	private String pass;
}

				


				<table>
					<tr th:if="${validationError}" th:each="error : ${validationError}">
						<td style="color: red;" th:text="${error}"></td>
					</tr>
				</table>
               <form class="register" th:action="register" th:object="${accountForm} method="post">

					<div class="Item">
						<label>id</label><input th:field="*{name}"></input>
					</div>

					<div class="Item">
						<label>password</label><input th:field="*{pass}"></input>
					</div>

					<input type="submit" name=""value="登録">
				</form>

				<p th:text="'id: ' + ${accountForm.name}" />
				<p th:text="'password: ' + ${accountForm.pass}" />

Answer 1

return先を修正した後SpringBootを再起動したら動作しました。