def update_essence(params = {})
      raise EssenceMissingError if essence.nil?
      if essence.update(params)
        return true
      else
        errors.add(:essence, :validation_failed)
        return false
      end
    end
def update_essence(params = {})
      raise EssenceMissingError if essence.nil?
      if essence.update(params)
        return true
      else
        errors.add(:essence, :validation_failed)
        return false
      end
    end
Updates the essence.

 Called from +Alchemy::Element#update_contents+

 Adds errors to self.base if essence validation fails.