freemarker.core.InvalidReferenceException: [... Exception message was already printed; see it above ...]
FreeMarker template error:
The following has evaluated to null or missing:
==> product [in template "product.html" at line 751, column 43]
FreeMarker模板误差：
以下已评估为null或丢失：
=产品“模板”产品HTML“在第751行，第43栏]
----------------------------
意思是有个值为null,就是不存在,
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)??
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)??
-----------------
提示：如果没有表达是合法的空/失踪，或者指定一个默认值myoptionalvar！mydefault，或使用< #如果myoptionalvar？？>在< #别的>当失踪/ # <<如果>>。（这些仅覆盖的表达；最后一步覆盖整个表达式，使用parenthessis：（myoptionvar。Foo）！mydefault，（myoptionvar。Foo）？？
大概意思是应该进行判断,对象是否为空
一般出现这种异常的原因为：如果对象为空，则freemarker就会抛出这个异常。
其实解决很简单，在用对象之前先判空，不空在进行属性的获取操作即可
