def set_link_keys *args
            @link_keys.clear if not @link_keys.empty?
            args.compact!
            args.each do |lf|
                @link_keys << lf
            end
            @link_value = @payload.select { |k,v| @link_keys.include? k }
        end
def set_link_keys *args
            @link_keys.clear if not @link_keys.empty?
            args.compact!
            args.each do |lf|
                @link_keys << lf
            end
            @link_value = @payload.select { |k,v| @link_keys.include? k }
        end
sets the links keys

 @param [Array] args list of keys to set

 \@link_value attribute will be updated