period_for_local (TZInfo::Timezone)

    # File lib/active_support/vendor/tzinfo-0.3.12/tzinfo/timezone.rb, line 334
        def period_for_local(local, dst = nil)
          results = periods_for_local(local)

          if results.empty?
            raise PeriodNotFound
          elsif results.size < 2
            results.first
          else
            # ambiguous result try to resolve

            if !dst.nil?
              matches = results.find_all {|period| period.dst? == dst}
              results = matches if !matches.empty?
            end

            if results.size < 2
              results.first
            else
              # still ambiguous, try the block

              if block_given?
                results = yield results
              end

              if results.is_a?(TimezonePeriod)
                results
              elsif results && results.size == 1
                results.first
              else
                raise AmbiguousTime, "#{local} is an ambiguous local time."
              end
            end
          end
        end