# File lib/zip/zip.rb, line 1797
    def create(name)
      field_class = nil
      ID_MAP.each { |id, klass|
        if klass.name == name
          field_class = klass
          break
        end
      }
      if ! field_class
        raise ZipError, "Unknown extra field '#{name}'"
      end
      self[name] = field_class.new()
    end