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https://issues.apache.org/jira/browse/VELTOOLS-139?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13014055#comment-13014055
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Nathan Bubna commented on VELTOOLS-139:
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Not just any undefined variable. Use $NULL or $null. If someone with access
to the context is putting in a non-null value with "NULL" or "null" as the key,
you have problems. In fact, my primary objection to the NullTool is the
implied/suggested key of $null. Terrible idea! Maybe an isNull(Object) method
could easily be added to the ContextTool (which does have a
$context.contains('var') method that is very close). But personally, i think
#if( $var == $null ) is very straightforward and cleaner than
$context.isNull($var).
> Bundle a NullTool in velocity Tools
> -----------------------------------
>
> Key: VELTOOLS-139
> URL: https://issues.apache.org/jira/browse/VELTOOLS-139
> Project: Velocity Tools
> Issue Type: Wish
> Components: GenericTools
> Affects Versions: 2.0
> Reporter: Vincent Massol
>
> Right now, in order to check for null we have to use:
> {code}#if ((! $var) && ("$!var" == "")){code}
> which is painful when you have lots of checks to do in several places.
> It would be nice either to have better null check support in velocity core or
> to bundle to NullTool in Velocity Tools:
> http://wiki.apache.org/velocity/NullTool
> I checked the user guide and googled around and couldn't find any simple way
> to check for null except using an undefined variable which I find way too
> magical and dangerous (what if someone defines that variable in the context).
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