def filter(request)
      found_field = request.every(@field).any? { |value| @value === value.to_s }
      return nil if !found_field && @mode == :select
      return nil if found_field && @mode == :reject
      request
    end
def filter(request)
      found_field = request.every(@field).any? { |value| @value === value.to_s }
      return nil if !found_field && @mode == :select
      return nil if found_field && @mode == :reject
      request
    end
Keep request if @mode == :select and request has the field and value.
 Drop request if @mode == :reject and request has the field and value.
 Returns nil otherwise.
 <tt>request</tt> Request Object