Rails - Feb 2006 - Nil in CSV Fixtures

The Guide to Testing the Rails 
http://manuals.rubyonrails.com/read/chapter/26#page65
says about CSV fixtures:

nulls can be achived by just placing a comma, for example, 
(1,sclaus,,false,) minus the parenthesis of course.

I tried that, but after the fixtures had been created, I checked the 
value of the field in the DB and instead of nil the value was zero, 
eventhough the default value for the field is NULL.
Is the guide wrong?

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