def exist?(key = nil)
      if key
        File.exist?(properties_filename) && File.exist?(content_filename(key))
      else
        File.exist?(properties_filename) && content?
      end
    end
def exist?(key = nil)
      if key
        File.exist?(properties_filename) && File.exist?(content_filename(key))
      else
        File.exist?(properties_filename) && content?
      end
    end
This object should not be constructed directly, but instead via
 {Gemstash::Storage#resource}.
 When +key+ is nil, this will test if this resource exists with any
 content. If a +key+ is provided, this will test that the resource exists
 with at least the given +key+ file. The +key+ corresponds to the +content+
 key provided to {#save}.

 @param key [Symbol, nil] the key of the content to check existence
 @return [Boolean] true if the indicated content exists