You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: activity.rb
    path of file: ./repos/openproject/config/constants/open_project
    
    the code of the file until where you have to start completion: #-- copyright
# OpenProject is an open source
    
      def register(event_type, options = {})
        options.assert_valid_keys(:class_name, :default)

        event_type = event_type.to_s
        available_event_types << event_type
        default_event_types << event_type unless options[:default] == false

        providers = options[:class_name] || event_type.classify
        self.providers[event_type] += Array(providers)
      end