Yes i think you are right, i put this because if some body reads code later on, then two methods <code>set_slug</code> and <code>set_slug_to_blank</code> come in order; so it seems little bit unusual.
Would it better if i put that if condition into separate private method.
Like  <code>
model_class.before_save :set_slug_to_blank, :if => :base_column_is_blank?
</code>