How to fail Velocity template processing with tracable message

Having:

• Velocity template or macro
• some object

How to validate the object (#if) and fail (stop further processing) in a way that is easily tracable to the place of failure (like throwing exception in Java).

I am looking for something like this:

#if ( ! $context.treasureMap.containsKey('gold'))
  #fail('no golden treasure here')
#end

Background

I am writing a maven site page. The velocity context is injected by maven and contains POM information. I want to test existence of some information from effective pom. When the information is not available, I want to fail.

Requirements

• fail Velocity processing > fail site generation > fail maven build.
• error message should lead to the place of failure so the site should be fixed
• preferably no configuration (no extensions, just constructs/tools contained in plain Velocity)

Tried

• Strict Reference Mode
  Unwanted configuration, do not want to fail on every occasion.
• #evaluate('#end') aka syntax error
  (Chose #end as most descriptive to my intent) Basically what I want. Fails the processing and maven build but the error message does not lead back to failure location: ParseException: Encountered "#end" at line 1, column 1..

The behavior was fixed in maven-doxia-sitetools:1.8.1 for my use case (see DOXIASITETOOLS-179).