Thymeleaf says Model attribute is null

michael.tillmanns :

This is my code where I add the model attributes :

List<String> errors = new ArrayList<>();

if(limit < 1 || limit > 1000) {
    errors.add("Das Feld Limit enthält keinen/einen ungültigen Wert.");
}

if(countryCode == null) {
    errors.add("Das Feld Ländercode enthält keinen/einen ungültigen Wert.");
}

model.addAttribute("errs", errors);

if(errors.size() > 0) {
    return "umsatzsteuerids";
}

And here is the HTML/Tyhemeleaf code where I try to use the model attribute:

<h3 th:if="${#lists.size(errs) != 0}">Folgende Fehler sind aufgetreten:</h3>
<table th:if="${#lists.size(errs) != 0}">
    <tbody>
    <tr th:each="error: ${errs}">
        <td th:text="${error}"></td>
    </tr>
    </tbody>
</table>

And this is the error I get once I try to request the web page:

java.lang.IllegalArgumentException: Cannot get list size of null
    at org.thymeleaf.util.Validate.notNull(Validate.java:37) ~[thymeleaf-3.0.11.RELEASE.jar:3.0.11.RELEASE]
    at org.thymeleaf.util.ListUtils.size(ListUtils.java:68) ~[thymeleaf-3.0.11.RELEASE.jar:3.0.11.RELEASE]
    at org.thymeleaf.expression.Lists.size(Lists.java:52) ~[thymeleaf-3.0.11.RELEASE.jar:3.0.11.RELEASE]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_242]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_242]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_242]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_242]
    at org.springframework.expression.spel.support.ReflectiveMethodExecutor.execute(ReflectiveMethodExecutor.java:129) ~[spring-expression-5.2.4.RELEASE.jar:5.2.4.RELEASE]
    at org.springframework.expression.spel.ast.MethodReference.getValueInternal(MethodReference.java:139) ~[spring-expression-5.2.4.RELEASE.jar:5.2.4.RELEASE]
    at org.springframework.expression.spel.ast.MethodReference.access$000(MethodReference.java:55) ~[spring-expression-5.2.4.RELEASE.jar:5.2.4.RELEASE]
    at org.springframework.expression.spel.ast.MethodReference$MethodValueRef.getValue(MethodReference.java:386) ~[spring-expression-5.2.4.RELEASE.jar:5.2.4.RELEASE]
    at org.springframework.expression.spel.ast.CompoundExpression.getValueInternal(CompoundExpression.java:92) ~[spring-expression-5.2.4.RELEASE.jar:5.2.4.RELEASE]
    at org.springframework.expression.spel.ast.OpNE.getValueInternal(OpNE.java:43) ~[spring-expression-5.2.4.RELEASE.jar:5.2.4.RELEASE]
    at org.springframework.expression.spel.ast.OpNE.getValueInternal(OpNE.java:33) ~[spring-expression-5.2.4.RELEASE.jar:5.2.4.RELEASE]
    at org.springframework.expression.spel.ast.SpelNodeImpl.getValue(SpelNodeImpl.java:112) ~[spring-expression-5.2.4.RELEASE.jar:5.2.4.RELEASE]
    at org.springframework.expression.spel.standard.SpelExpression.getValue(SpelExpression.java:337) ~[spring-expression-5.2.4.RELEASE.jar:5.2.4.RELEASE]
    at org.thymeleaf.spring5.expression.SPELVariableExpressionEvaluator.evaluate(SPELVariableExpressionEvaluator.java:263) ~[thymeleaf-spring5-3.0.11.RELEASE.jar:3.0.11.RELEASE]
    at org.thymeleaf.standard.expression.VariableExpression.executeVariableExpression(VariableExpression.java:166) ~[thymeleaf-3.0.11.RELEASE.jar:3.0.11.RELEASE]
    at org.thymeleaf.standard.expression.SimpleExpression.executeSimple(SimpleExpression.java:66) ~[thymeleaf-3.0.11.RELEASE.jar:3.0.11.RELEASE]
    at org.thymeleaf.standard.expression.Expression.execute(Expression.java:109) ~[thymeleaf-3.0.11.RELEASE.jar:3.0.11.RELEASE]
    at org.thymeleaf.standard.expression.Expression.execute(Expression.java:138) ~[thymeleaf-3.0.11.RELEASE.jar:3.0.11.RELEASE]
    at org.thymeleaf.standard.expression.Expression.execute(Expression.java:125) ~[thymeleaf-3.0.11.RELEASE.jar:3.0.11.RELEASE]
    at org.thymeleaf.standard.processor.StandardIfTagProcessor.isVisible(StandardIfTagProcessor.java:59) ~[thymeleaf-3.0.11.RELEASE.jar:3.0.11.RELEASE]
    at org.thymeleaf.standard.processor.AbstractStandardConditionalVisibilityTagProcessor.doProcess(AbstractStandardConditionalVisibilityTagProcessor.java:61) ~[thymeleaf-3.0.11.RELEASE.jar:3.0.11.RELEASE]
    at org.thymeleaf.processor.element.AbstractAttributeTagProcessor.doProcess(AbstractAttributeTagProcessor.java:74) ~[thymeleaf-3.0.11.RELEASE.jar:3.0.11.RELEASE]
    at org.thymeleaf.processor.element.AbstractElementTagProcessor.process(AbstractElementTagProcessor.java:95) ~[thymeleaf-3.0.11.RELEASE.jar:3.0.11.RELEASE]
    at org.thymeleaf.util.ProcessorConfigurationUtils$ElementTagProcessorWrapper.process(ProcessorConfigurationUtils.java:633) ~[thymeleaf-3.0.11.RELEASE.jar:3.0.11.RELEASE]
    at org.thymeleaf.engine.ProcessorTemplateHandler.handleOpenElement(ProcessorTemplateHandler.java:1314) ~[thymeleaf-3.0.11.RELEASE.jar:3.0.11.RELEASE]
    at org.thymeleaf.engine.OpenElementTag.beHandled(OpenElementTag.java:205) ~[thymeleaf-3.0.11.RELEASE.jar:3.0.11.RELEASE]
    at org.thymeleaf.engine.TemplateModel.process(TemplateModel.java:136) ~[thymeleaf-3.0.11.RELEASE.jar:3.0.11.RELEASE]
    at org.thymeleaf.engine.TemplateManager.parseAndProcess(TemplateManager.java:661) ~[thymeleaf-3.0.11.RELEASE.jar:3.0.11.RELEASE]
    at org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1098) ~[thymeleaf-3.0.11.RELEASE.jar:3.0.11.RELEASE]
    at org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1072) ~[thymeleaf-3.0.11.RELEASE.jar:3.0.11.RELEASE]
    at org.thymeleaf.spring5.view.ThymeleafView.renderFragment(ThymeleafView.java:362) ~[thymeleaf-spring5-3.0.11.RELEASE.jar:3.0.11.RELEASE]
    at org.thymeleaf.spring5.view.ThymeleafView.render(ThymeleafView.java:189) ~[thymeleaf-spring5-3.0.11.RELEASE.jar:3.0.11.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1373) ~[spring-webmvc-5.2.4.RELEASE.jar:5.2.4.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1118) ~[spring-webmvc-5.2.4.RELEASE.jar:5.2.4.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1057) ~[spring-webmvc-5.2.4.RELEASE.jar:5.2.4.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943) ~[spring-webmvc-5.2.4.RELEASE.jar:5.2.4.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.2.4.RELEASE.jar:5.2.4.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898) ~[spring-webmvc-5.2.4.RELEASE.jar:5.2.4.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:634) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.2.4.RELEASE.jar:5.2.4.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.31.jar:9.0.31]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.2.4.RELEASE.jar:5.2.4.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.4.RELEASE.jar:5.2.4.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.2.4.RELEASE.jar:5.2.4.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.4.RELEASE.jar:5.2.4.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.2.4.RELEASE.jar:5.2.4.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.4.RELEASE.jar:5.2.4.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) ~[tomcat-embed-core-9.0.31.jar:9.0.31]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-9.0.31.jar:9.0.31]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541) [tomcat-embed-core-9.0.31.jar:9.0.31]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) [tomcat-embed-core-9.0.31.jar:9.0.31]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) [tomcat-embed-core-9.0.31.jar:9.0.31]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) [tomcat-embed-core-9.0.31.jar:9.0.31]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) [tomcat-embed-core-9.0.31.jar:9.0.31]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:367) [tomcat-embed-core-9.0.31.jar:9.0.31]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) [tomcat-embed-core-9.0.31.jar:9.0.31]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868) [tomcat-embed-core-9.0.31.jar:9.0.31]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1639) [tomcat-embed-core-9.0.31.jar:9.0.31]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-9.0.31.jar:9.0.31]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_242]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_242]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.31.jar:9.0.31]
    at java.lang.Thread.run(Thread.java:748) [na:1.8.0_242]

I have already read some stuff on the internet, i.e. I already tried to use the @ModelAttribute annotation on the Controller RequestMapping method.

Also it worked with everything just not with this list of strings for some reason...

Thanks in advance.

Sudhir Ojha :

Use isEmpty(). It will handle null and size 0.

<h3 th:if="${not #lists.isEmpty(errs)}">Folgende Fehler sind aufgetreten:</h3>
<table th:if="${not #lists.isEmpty(errs)}">
    <tbody>
    <tr th:each="error: ${errs}">
        <td th:text="${error}"></td>
    </tr>
    </tbody>
</table>