freemarker报错：Tip: If the failing expression is known to be legally null/missing, either specify a de

freemarker报错：Tip: If the failing expression is known to be legally null/missing, either specify a default value with 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 parenthessis: (myOptionVar.foo)!myDefault, (myOptionVar.foo)??

大致意思是所写的表达式应判定不为空或者指定一个默认值，貌似ftl的<#if>判断一般都一定要判断一下不能为空

错误写法（后台会报错，实际上可以允许）：

</pre><p><pre name="code" class="html"><span style="font-size:18px;"><#if lists?? && lists?size gt 0>
<#list lists as list>
<option value="${list.id}" <#if outbean.id == '${list.id}'> selected="selected" </#if> >${list.name!''}</option>
</#list>
</#if></span>

纠正写法：

<#if lists?? && lists?size gt 0>
<#list lists as list>
<option value="${list.id}" <#if (outbean.id!'') == '${list.id}'> selected="selected" </#if> >${list.name!''}</option>
</#list>
</#if>