# File lib/vcr/cassette/persisters.rb, line 17
      def [](name)
        @persisters.fetch(name) do |_|
          @persisters[name] = case name
            when :file_system then FileSystem
            else raise ArgumentError, "The requested VCR cassette persister " +
                                      "(#{name.inspect}) is not registered."
          end
        end
      end