상품등록폼 강의 중 등록하기 누르면 500에러가 뜹니

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item.html 파일입니다

<!DOCTYPE HTML>
<html xmlns:th="http://www.thymeleaf.org">
<head>
<meta charset="utf-8">
<link href="../css/bootstrap.min.css"
th:href="@{/css/bootstrap.min.css}" rel="stylesheet">
<style>
.container {
max-width: 560px;
}
</style>
</head>
<body>
<div class="container">
<div class="py-5 text-center">
<h2>상품 상세</h2>
</div>
<div>
<label for="itemId">상품 ID</label>
<input type="text" id="itemId" name="itemId" class="form-control"
value="1" th:value="${item.id}" readonly>
</div>
<div>
<label for="itemName">상품명</label>
<input type="text" id="itemName" name="itemName" class="form-control"
value="상품A" th:value="${item.itemName}" readonly>
</div>
<div>
<label for="price">가격</label>
<input type="text" id="price" name="price" class="form-control"
value="10000" th:value="${item.price}" readonly>
</div>
<div>
<label for="quantity">수량</label>
<input type="text" id="quantity" name="quantity" class="form-control"
value="10" th:value="${item.quantity}" readonly>
</div>
<hr class="my-4">
<div class="row">
<div class="col">
<button class="w-100 btn btn-primary btn-lg"
onclick="location.href='editForm.html'"
th:onclick="|location.href='@{/basic/items/{itemId}/
edit(itemId=${item.id})}'|" type="button">상품 수정</button>
</div>
<div class="col">
<button class="w-100 btn btn-secondary btn-lg"
onclick="location.href='items.html'"
th:onclick="|location.href='@{/basic/items}'|"
type="button">목록으로</button>
</div>
</div>
</div> 
</body>
</html>

basicitemcontroller입니다

@GetMapping("/add")
public String addForm() {
return "basic/addForm";
}

@PostMapping("/add")
public String save(@RequestParam String itemName,
@RequestParam int price,
@RequestParam Integer quantity,
Model model) {

Item item = new Item();
item.setItemName(itemName);
item.setPrice(price);
item.setQuantity(quantity);

itemRepository.save(item);

return "basic/item";
}

로그입니다

2023-09-05 17:57:38.461 ERROR 7144 --- [nio-8080-exec-2] org.thymeleaf.TemplateEngine : [THYMELEAF][http-nio-8080-exec-2] Exception processing template "basic/item": Exception evaluating SpringEL expression: "item.id" (template: "basic/item" - line 21, col 22)

org.thymeleaf.exceptions.TemplateProcessingException: Exception evaluating SpringEL expression: "item.id" (template: "basic/item" - line 21, col 22)

at org.thymeleaf.spring5.expression.SPELVariableExpressionEvaluator.evaluate(SPELVariableExpressionEvaluator.java:292) ~[thymeleaf-spring5-3.0.15.RELEASE.jar:3.0.15.RELEASE]

at org.thymeleaf.standard.expression.VariableExpression.executeVariableExpression(VariableExpression.java:166) ~[thymeleaf-3.0.15.RELEASE.jar:3.0.15.RELEASE]

at org.thymeleaf.standard.expression.SimpleExpression.executeSimple(SimpleExpression.java:66) ~[thymeleaf-3.0.15.RELEASE.jar:3.0.15.RELEASE]

at org.thymeleaf.standard.expression.Expression.execute(Expression.java:109) ~[thymeleaf-3.0.15.RELEASE.jar:3.0.15.RELEASE]

at org.thymeleaf.standard.expression.Expression.execute(Expression.java:138) ~[thymeleaf-3.0.15.RELEASE.jar:3.0.15.RELEASE]

at org.thymeleaf.standard.processor.AbstractStandardExpressionAttributeTagProcessor.doProcess(AbstractStandardExpressionAttributeTagProcessor.java:144) ~[thymeleaf-3.0.15.RELEASE.jar:3.0.15.RELEASE]

at org.thymeleaf.processor.element.AbstractAttributeTagProcessor.doProcess(AbstractAttributeTagProcessor.java:74) ~[thymeleaf-3.0.15.RELEASE.jar:3.0.15.RELEASE]

at org.thymeleaf.processor.element.AbstractElementTagProcessor.process(AbstractElementTagProcessor.java:95) ~[thymeleaf-3.0.15.RELEASE.jar:3.0.15.RELEASE]

at org.thymeleaf.util.ProcessorConfigurationUtils$ElementTagProcessorWrapper.process(ProcessorConfigurationUtils.java:633) ~[thymeleaf-3.0.15.RELEASE.jar:3.0.15.RELEASE]

at org.thymeleaf.engine.ProcessorTemplateHandler.handleStandaloneElement(ProcessorTemplateHandler.java:918) ~[thymeleaf-3.0.15.RELEASE.jar:3.0.15.RELEASE]

at org.thymeleaf.engine.StandaloneElementTag.beHandled(StandaloneElementTag.java:228) ~[thymeleaf-3.0.15.RELEASE.jar:3.0.15.RELEASE]

at org.thymeleaf.engine.TemplateModel.process(TemplateModel.java:136) ~[thymeleaf-3.0.15.RELEASE.jar:3.0.15.RELEASE]

at org.thymeleaf.engine.TemplateManager.parseAndProcess(TemplateManager.java:661) ~[thymeleaf-3.0.15.RELEASE.jar:3.0.15.RELEASE]

at org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1098) ~[thymeleaf-3.0.15.RELEASE.jar:3.0.15.RELEASE]

at org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1072) ~[thymeleaf-3.0.15.RELEASE.jar:3.0.15.RELEASE]

at org.thymeleaf.spring5.view.ThymeleafView.renderFragment(ThymeleafView.java:366) ~[thymeleaf-spring5-3.0.15.RELEASE.jar:3.0.15.RELEASE]

at org.thymeleaf.spring5.view.ThymeleafView.render(ThymeleafView.java:190) ~[thymeleaf-spring5-3.0.15.RELEASE.jar:3.0.15.RELEASE]

at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1406) ~[spring-webmvc-5.3.29.jar:5.3.29]

at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1150) ~[spring-webmvc-5.3.29.jar:5.3.29]

at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1089) ~[spring-webmvc-5.3.29.jar:5.3.29]

at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:965) ~[spring-webmvc-5.3.29.jar:5.3.29]

at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.3.29.jar:5.3.29]

at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:909) ~[spring-webmvc-5.3.29.jar:5.3.29]

at javax.servlet.http.HttpServlet.service(HttpServlet.java:555) ~[tomcat-embed-core-9.0.79.jar:4.0.FR]

at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.3.29.jar:5.3.29]

at javax.servlet.http.HttpServlet.service(HttpServlet.java:623) ~[tomcat-embed-core-9.0.79.jar:4.0.FR]

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:209) ~[tomcat-embed-core-9.0.79.jar:9.0.79]

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153) ~[tomcat-embed-core-9.0.79.jar:9.0.79]

at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51) ~[tomcat-embed-websocket-9.0.79.jar:9.0.79]

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178) ~[tomcat-embed-core-9.0.79.jar:9.0.79]

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153) ~[tomcat-embed-core-9.0.79.jar:9.0.79]

at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.3.29.jar:5.3.29]

at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.29.jar:5.3.29]

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178) ~[tomcat-embed-core-9.0.79.jar:9.0.79]

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153) ~[tomcat-embed-core-9.0.79.jar:9.0.79]

at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.3.29.jar:5.3.29]

at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.29.jar:5.3.29]

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178) ~[tomcat-embed-core-9.0.79.jar:9.0.79]

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153) ~[tomcat-embed-core-9.0.79.jar:9.0.79]

at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.3.29.jar:5.3.29]

at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.29.jar:5.3.29]

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178) ~[tomcat-embed-core-9.0.79.jar:9.0.79]

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153) ~[tomcat-embed-core-9.0.79.jar:9.0.79]

at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:167) ~[tomcat-embed-core-9.0.79.jar:9.0.79]

at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:90) ~[tomcat-embed-core-9.0.79.jar:9.0.79]

at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:481) ~[tomcat-embed-core-9.0.79.jar:9.0.79]

at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:130) ~[tomcat-embed-core-9.0.79.jar:9.0.79]

at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:93) ~[tomcat-embed-core-9.0.79.jar:9.0.79]

at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) ~[tomcat-embed-core-9.0.79.jar:9.0.79]

at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) ~[tomcat-embed-core-9.0.79.jar:9.0.79]

at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:390) ~[tomcat-embed-core-9.0.79.jar:9.0.79]

at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:63) ~[tomcat-embed-core-9.0.79.jar:9.0.79]

at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:926) ~[tomcat-embed-core-9.0.79.jar:9.0.79]

at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1790) ~[tomcat-embed-core-9.0.79.jar:9.0.79]

at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:52) ~[tomcat-embed-core-9.0.79.jar:9.0.79]

at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191) ~[tomcat-embed-core-9.0.79.jar:9.0.79]

at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659) ~[tomcat-embed-core-9.0.79.jar:9.0.79]

at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) ~[tomcat-embed-core-9.0.79.jar:9.0.79]

at java.base/java.lang.Thread.run(Thread.java:831) ~[na:na]

Caused by: org.springframework.expression.spel.SpelEvaluationException: EL1007E: Property or field 'id' cannot be found on null

at org.springframework.expression.spel.ast.PropertyOrFieldReference.readProperty(PropertyOrFieldReference.java:219) ~[spring-expression-5.3.29.jar:5.3.29]

at org.springframework.expression.spel.ast.PropertyOrFieldReference.getValueInternal(PropertyOrFieldReference.java:106) ~[spring-expression-5.3.29.jar:5.3.29]

at org.springframework.expression.spel.ast.PropertyOrFieldReference.access$000(PropertyOrFieldReference.java:53) ~[spring-expression-5.3.29.jar:5.3.29]

at org.springframework.expression.spel.ast.PropertyOrFieldReference$AccessorLValue.getValue(PropertyOrFieldReference.java:412) ~[spring-expression-5.3.29.jar:5.3.29]

at org.springframework.expression.spel.ast.CompoundExpression.getValueInternal(CompoundExpression.java:93) ~[spring-expression-5.3.29.jar:5.3.29]

at org.springframework.expression.spel.ast.SpelNodeImpl.getValue(SpelNodeImpl.java:114) ~[spring-expression-5.3.29.jar:5.3.29]

at org.springframework.expression.spel.standard.SpelExpression.getValue(SpelExpression.java:338) ~[spring-expression-5.3.29.jar:5.3.29]

at org.thymeleaf.spring5.expression.SPELVariableExpressionEvaluator.evaluate(SPELVariableExpressionEvaluator.java:265) ~[thymeleaf-spring5-3.0.15.RELEASE.jar:3.0.15.RELEASE]

... 58 common frames omitted

2023-09-05 17:57:38.463 ERROR 7144 --- [nio-8080-exec-2] o.a.c.c.C.[.[.[/].[dispatcherServlet] : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.thymeleaf.exceptions.TemplateProcessingException: Exception evaluating SpringEL expression: "item.id" (template: "basic/item" - line 21, col 22)] with root cause

org.springframework.expression.spel.SpelEvaluationException: EL1007E: Property or field 'id' cannot be found on null