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: plain.rb
    path of file: ./repos/truffleruby/lib/gems/gems/net-imap-0.3.4/lib/net/imap/authenticators
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

# Authenticator for the "+PLAIN+" SASL mechanism, specified in
# RFC4616[https://tools.ietf.org/ht
    
  def initialize(username, password, authzid: nil)
    raise ArgumentError, "username contains NULL" if username&.include?(NULL)
    raise ArgumentError, "password contains NULL" if password&.include?(NULL)
    raise ArgumentError, "authzid  contains NULL" if authzid&.include?(NULL)
    @username = username
    @password = password
    @authzid  = authzid
  end