Rails3 undefined method `zero?' for nil:NilClass -- statssample override's Rail's Enumerable.sum

This issue 

http://stackoverflow.com/questions/8899272/rails-3-undefined-method-zero-for-nilnilclass-in-many-to-many-relationsh
http://stackoverflow.com/questions/9289535/rails-3-2-uniqueness-validation-raises-undefined-method-zero-for-nilnilclass

also seems to affect this gem when using this within Rails 3.  

Is there a workaround?
