debug|freemarker的InvalidReferenceException处理

用freemarker的时候，报了个异常，如下：

FreeMarker template error:
The following has evaluated to null or missing:
==> setmeal.remark  [in template "mobile_setmeal_detail.ftl" at line 34, column 37]
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Tip: It's the step after the last dot that caused this error, not those before it.
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Tip: If the failing expression is known to be 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. (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: ${setmeal.remark}  [in template "mobile_setmeal_detail.ftl" at line 34, column 35]
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Java stack trace (for programmers):
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freemarker.core.InvalidReferenceException: [... Exception message was already printed; see it above ...]
    at freemarker.core.InvalidReferenceException.getInstance(InvalidReferenceException.java:131)
    at freemarker.core.EvalUtil.coerceModelToString(EvalUtil.java:355)

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密密麻麻的，真让人头疼，先检查下环境配的对不对好了，xml配置、模板地址啥的，检查后发现没问题，那进入到第二步，检查下具体异常是啥；

首先找下抛出的异常是啥，InvalidReferenceException，好的，百度一下这个异常咋回事，一搜，说是模板里面的放的值不能为空，好家伙，不能为空啊，那读读报的错是不是这个意思呢？看到异常里面写到：The following has evaluated to null or missing，说是下面有个字段为空了，所以不行，好家伙，看来真的是这个原因，下面还有俩tip，读一读：

Tip: If the failing expression is known to be 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. (These only cover the last step of the expression; to cover the whole expression, use parenthesis: (myOptionalVar.foo)!myDefault, (myOptionalVar.foo)??

 如果出错的表达式（就是我设置的setmeal.remark），引用了个空的值，那么可以这么做.....balabalblabla（不翻译了，比较懒）

 读了读下面的报错，基本上明白错误的地方了：就是我用于生成模板的数据，有些是空字段，而这个我并没有设置，因此模板引擎报错了。知道这个错误后事情就简单了，要么设置空字段默认值，要么传入的值不能为空即可。