def [](uri, factory = nil)
      data = store[uri]
      data.nil? ? nil : Aspire::Object::User.new(uri, factory, json: data)
    end
def [](uri, factory = nil)
      data = store[uri]
      data.nil? ? nil : Aspire::Object::User.new(uri, factory, json: data)
    end
Initialises a new UserLookup instance
 @see (Hash#initialize)
 @param filename [String] the filename of the CSV file to populate the hash
 @return [void]
 Returns an Aspire::Object::User instance for a URI
 @param uri [String] the URI of the user
 @param factory [Aspire::Object::Factory] the data object factory
 @return [Aspire::Object::User] the user