Jsf 2 无法达到目标'；用户'；有时返回null]

我有一个显示对话框的链接，如下所示：

<h:form>
    <div class="btn-alt" id="#signupStart">
        <h:commandLink action="#{signUpBean.displaySignUpScreenAction()}">#{msg['action.createaccount']}
        <f:ajax onevent="function(data) {if (data.status == 'success') {$('#signUpDialog').dialog('open');startGA();} }"  render=":signupform"/>
        </h:commandLink>
    </div>
</h:form>

<h:form id="signupform" title="#{msg['action.createaccount']}"><input type="hidden" autofocus="autofocus" />

    <div style="position: relative;">                       
        <h:inputText maxlength="50" id="txtFirstName" placeholder="#{msg['firstname']}" value="#{signUpBean.user.firstName}" styleClass="#{component.valid?'':'field-error'}" title="#{msg['firstname']}">
            <f:ajax event="blur" render="txtFirstName messages"/>                       
        </h:inputText>
    </div>

</h:form>

单击show dialog链接，我创建用户对象，然后渲染对话框，因此绑定应该可以正常工作，实际上它可以正常工作，但有时在生产服务器上，我会在日志中看到错误，如：

value="#{signUpBean.user.firstName}": Target Unreachable, 'user' returned null] with root cause 
Jun 09 17:04:03 myapp i-e38b9c8c: javax.el.PropertyNotFoundException: Target Unreachable, 'user' returned null 
Jun 09 17:04:03 myapp i-e38b9c8c: at org.apache.el.parser.AstValue.getTarget(AstValue.java:147) 
Jun 09 17:04:03 myapp i-e38b9c8c: at org.apache.el.parser.AstValue.getType(AstValue.java:81) 
Jun 09 17:04:03 myapp i-e38b9c8c: at org.apache.el.ValueExpressionImpl.getType(ValueExpressionImpl.java:171) 
Jun 09 17:04:03 myapp i-e38b9c8c: at com.sun.faces.facelets.el.TagValueExpression.getType(TagValueExpression.java:98) 
Jun 09 17:04:03 myapp i-e38b9c8c: at com.sun.faces.renderkit.html_basic.HtmlBasicInputRenderer.getConvertedValue(HtmlBasicInputRenderer.java:95) 
Jun 09 17:04:03 myapp i-e38b9c8c: at javax.faces.component.UIInput.getConvertedValue(UIInput.java:1046) 
Jun 09 17:04:03 myapp i-e38b9c8c: at javax.faces.component.UIInput.validate(UIInput.java:976) 
Jun 09 17:04:03 myapp i-e38b9c8c: at javax.faces.component.UIInput.executeValidate(UIInput.java:1249) 
Jun 09 17:04:03 myapp i-e38b9c8c: at javax.faces.component.UIInput.processValidators(UIInput.java:712) 
Jun 09 17:04:03 myapp i-e38b9c8c: at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:1258) 
Jun 09 17:04:03 myapp i-e38b9c8c: at javax.faces.component.UIForm.processValidators(UIForm.java:253) 
Jun 09 17:04:03 myapp i-e38b9c8c: at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:1258) 
Jun 09 17:04:03 myapp i-e38b9c8c: at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:1258) 
Jun 09 17:04:03 myapp i-e38b9c8c: at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:1258) 
Jun 09 17:04:03 myapp i-e38b9c8c: at javax.faces.component.UIViewRoot.processValidators(UIViewRoot.java:1195) 
Jun 09 17:04:03 myapp i-e38b9c8c: at com.sun.faces.lifecycle.ProcessValidationsPhase.execute(ProcessValidationsPhase.java:76) 
Jun 09 17:04:03 myapp i-e38b9c8c: at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101) 
Jun 09 17:04:03 myapp i-e38b9c8c: at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:198) 
Jun 09 17:04:03 myapp i-e38b9c8c: at javax.faces.webapp.FacesServlet.service(FacesServlet.java:646) 
Jun 09 17:04:03 myapp i-e38b9c8c: at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303) 
Jun 09 17:04:03 myapp i-e38b9c8c: at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) 
Jun 09 17:04:03 myapp i-e38b9c8c: at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) 
Jun 09 17:04:03 myapp i-e38b9c8c: at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241) 
Jun 09 17:04:03 myapp i-e38b9c8c: at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) 
Jun 09 17:04:03 myapp i-e38b9c8c: at org.apache.shiro.web.servlet.AbstractShiroFilter.executeChain(AbstractShiroFilter.java:449) 
Jun 09 17:04:03 myapp i-e38b9c8c: at org.apache.shiro.web.servlet.AbstractShiroFilter$1.call(AbstractShiroFilter.java:365) 
Jun 09 17:04:03 myapp i-e38b9c8c: at org.apache.shiro.subject.support.SubjectCallable.doCall(SubjectCallable.java:90) 
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我使用的是JSF2.2，请告知为什么有时会出现此错误以及如何解决。

显示您的ManagedBeancode@TiagoVieira Dos Santos，要显示的代码，我已经显示了init的重要部分。您的用户对象属性和getter。你有什么构造方法吗？如果您尝试将用户对象初始化一切正常，我为用户对象和用户对象内的属性设置了setter和getter，只是这个错误我无法重现，但有时我会在日志中找到它。

value="#{signUpBean.user.firstName}": Target Unreachable, 'user' returned null] with root cause 
Jun 09 17:04:03 myapp i-e38b9c8c: javax.el.PropertyNotFoundException: Target Unreachable, 'user' returned null 
Jun 09 17:04:03 myapp i-e38b9c8c: at org.apache.el.parser.AstValue.getTarget(AstValue.java:147) 
Jun 09 17:04:03 myapp i-e38b9c8c: at org.apache.el.parser.AstValue.getType(AstValue.java:81) 
Jun 09 17:04:03 myapp i-e38b9c8c: at org.apache.el.ValueExpressionImpl.getType(ValueExpressionImpl.java:171) 
Jun 09 17:04:03 myapp i-e38b9c8c: at com.sun.faces.facelets.el.TagValueExpression.getType(TagValueExpression.java:98) 
Jun 09 17:04:03 myapp i-e38b9c8c: at com.sun.faces.renderkit.html_basic.HtmlBasicInputRenderer.getConvertedValue(HtmlBasicInputRenderer.java:95) 
Jun 09 17:04:03 myapp i-e38b9c8c: at javax.faces.component.UIInput.getConvertedValue(UIInput.java:1046) 
Jun 09 17:04:03 myapp i-e38b9c8c: at javax.faces.component.UIInput.validate(UIInput.java:976) 
Jun 09 17:04:03 myapp i-e38b9c8c: at javax.faces.component.UIInput.executeValidate(UIInput.java:1249) 
Jun 09 17:04:03 myapp i-e38b9c8c: at javax.faces.component.UIInput.processValidators(UIInput.java:712) 
Jun 09 17:04:03 myapp i-e38b9c8c: at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:1258) 
Jun 09 17:04:03 myapp i-e38b9c8c: at javax.faces.component.UIForm.processValidators(UIForm.java:253) 
Jun 09 17:04:03 myapp i-e38b9c8c: at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:1258) 
Jun 09 17:04:03 myapp i-e38b9c8c: at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:1258) 
Jun 09 17:04:03 myapp i-e38b9c8c: at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:1258) 
Jun 09 17:04:03 myapp i-e38b9c8c: at javax.faces.component.UIViewRoot.processValidators(UIViewRoot.java:1195) 
Jun 09 17:04:03 myapp i-e38b9c8c: at com.sun.faces.lifecycle.ProcessValidationsPhase.execute(ProcessValidationsPhase.java:76) 
Jun 09 17:04:03 myapp i-e38b9c8c: at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101) 
Jun 09 17:04:03 myapp i-e38b9c8c: at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:198) 
Jun 09 17:04:03 myapp i-e38b9c8c: at javax.faces.webapp.FacesServlet.service(FacesServlet.java:646) 
Jun 09 17:04:03 myapp i-e38b9c8c: at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303) 
Jun 09 17:04:03 myapp i-e38b9c8c: at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) 
Jun 09 17:04:03 myapp i-e38b9c8c: at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) 
Jun 09 17:04:03 myapp i-e38b9c8c: at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241) 
Jun 09 17:04:03 myapp i-e38b9c8c: at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) 
Jun 09 17:04:03 myapp i-e38b9c8c: at org.apache.shiro.web.servlet.AbstractShiroFilter.executeChain(AbstractShiroFilter.java:449) 
Jun 09 17:04:03 myapp i-e38b9c8c: at org.apache.shiro.web.servlet.AbstractShiroFilter$1.call(AbstractShiroFilter.java:365) 
Jun 09 17:04:03 myapp i-e38b9c8c: at org.apache.shiro.subject.support.SubjectCallable.doCall(SubjectCallable.java:90) 
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