98. Error s.e.errormvcautoconfiguration $staticview reported by freemaker framework: cannot render error page for request

  Error message

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]
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Back end code

The front-end code

  Its function is to realize the drop-down box , Added option But it doesn't show （ Here's the picture ）, And the back-end data has been obtained （ It's printed on the console ）, I thought I couldn't get data from the front-end .

 

Look back and report the wrong information , Find out

 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:

The general meaning is ：Servlet Request processing failed , May be null or missing

Problem analysis

That should be the problem of null value , As a result, the drop-down box cannot be displayed normally ,teacherNames There is a null value in

Log The treatment method is given, that is （ Red and bold tips above ） add to

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

            </div>

Later, the final solution was found by searching ：

Problem solving

In the configuration item （application.yml） Add the setting of global de null value in ：

spring.freemarker.settings.classic_compatible= true

Be careful true There is a space in front , Otherwise it won't work . 

Final effect

 

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