九十八、freemarker框架报错 s.e.ErrorMvcAutoConfiguration$StaticView : Cannot render error page for request

 报错信息

2022-04-22 12:59:38.904 ERROR 16164 --- [nio-8888-exec-1] freemarker.runtime                       : Error executing FreeMarker template

freemarker.core.InvalidReferenceException: The following has evaluated to null or missing:
==> pageContext  [in template "courseAdd.html" at line 84, column 29]

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Tip: If the failing expression is known to legally refer to something that's sometimes null or missing, either specify a default value like myOptionalVar!myDefault, or use <#if myOptionalVar??>when-present<#else>when-missing</#if>. (These only cover the last step of the expression; to cover the whole expression, use parenthesis: (myOptionalVar.foo)!myDefault, (myOptionalVar.foo)??
----

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FTL stack trace ("~" means nesting-related):
    - Failed at: ${pageContext.request.contextPath}  [in template "courseAdd.html" at line 84, column 27]
----
 

后端代码

前端代码

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 其功能要实现下拉框，添加了option却显示不出来（如下图），并且后端数据已经拿到（打印在控制台了），心想就是前端这里拿不到数据。

回头看报错信息，发现

 o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is freemarker.core.InvalidReferenceException: The following has evaluated to null or missing:

大致意思为：Servlet请求处理失败，可能为空值或缺失值

问题分析

那应该就是空值的问题，导致下拉框无法正常显示，teacherNames中存在空值

看日志 给出了处理办法即（上方标红加粗的提示） 添加

            <div class="layui-input-block">
<!--                <#if myOptionalVar??>when-present<#else>when-missing</#if>-->
                <select id="baseCourseSelect" lay-search>
                    <option>--请选择——</option>
                        <#list teacherNames as tname>
                    <option value="${tname}">${tname}</option>
                        </#list>
                </select>

            </div>

后来通过查找找到了最终解决方法：

问题解决

在配置项（application.yml）中加入全局去空值的设置：

spring.freemarker.settings.classic_compatible= true

注意 true 前面有一个空格，不然不会生效。 

最终效果

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