def join_values(operator, return_value)
      leader = LEADERS.fetch(operator, '')
      joiner = JOINERS.fetch(operator, ',')
      case operator
      when '&', '?'
        leader + return_value.map{|k,v|
          if v.is_a?(Array) && v.first =~ /=/
            v.join(joiner)
          elsif v.is_a?(Array)
            v.map{|inner_value| "#{k}=#{inner_value}"}.join(joiner)
          else
            "#{k}=#{v}"
          end
        }.join(joiner)
      when ';'
        return_value.map{|k,v|
          if v.is_a?(Array) && v.first =~ /=/
            ';' + v.join(";")
          elsif v.is_a?(Array)
            ';' + v.map{|inner_value| "#{k}=#{inner_value}"}.join(";")
          else
            v && v != '' ?  ";#{k}=#{v}" : ";#{k}"
          end
        }.join
      else
        leader + return_value.map{|k,v| v}.join(joiner)
      end
    end
def join_values(operator, return_value)
      leader = LEADERS.fetch(operator, '')
      joiner = JOINERS.fetch(operator, ',')
      case operator
      when '&', '?'
        leader + return_value.map{|k,v|
          if v.is_a?(Array) && v.first =~ /=/
            v.join(joiner)
          elsif v.is_a?(Array)
            v.map{|inner_value| "#{k}=#{inner_value}"}.join(joiner)
          else
            "#{k}=#{v}"
          end
        }.join(joiner)
      when ';'
        return_value.map{|k,v|
          if v.is_a?(Array) && v.first =~ /=/
            ';' + v.join(";")
          elsif v.is_a?(Array)
            ';' + v.map{|inner_value| "#{k}=#{inner_value}"}.join(";")
          else
            v && v != '' ?  ";#{k}=#{v}" : ";#{k}"
          end
        }.join
      else
        leader + return_value.map{|k,v| v}.join(joiner)
      end
    end
Takes a set of values, and joins them together based on the
 operator.

 @param [String, Nil] operator One of the operators from the set
   (?,&,+,#,;,/,.), or nil if there wasn't one.
 @param [Array] return_value
   The set of return values (as [variable_name, value] tuples) that will
   be joined together.

 @return [String] The transformed mapped value