def assert_valid_links(links)
      if links.empty?
        raise ArgumentError, '+options[:links]+ should not be empty'
      end

      links.each do |link|
        case link
          when Symbol, String
            unless @relationships.named?(link.to_sym)
              raise ArgumentError, "+options[:links]+ entry #{link.inspect} does not map to a relationship in #{model}"
            end
        end
      end
    end
def assert_valid_links(links)
      if links.empty?
        raise ArgumentError, '+options[:links]+ should not be empty'
      end

      links.each do |link|
        case link
          when Symbol, String
            unless @relationships.named?(link.to_sym)
              raise ArgumentError, "+options[:links]+ entry #{link.inspect} does not map to a relationship in #{model}"
            end
        end
      end
    end
Verifies that value of :links option
 refers to existing associations

 @api private