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: setting.rb
    path of file: ./repos/sail/app/models/sail
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

require "fugit"

module Sail
  # Setting
  # This is the model used for settings
  # it
    
    def model_exists
      errors.add(:invalid_model, "Model does not exist") unless AVAILABLE_MODELS.include?(value)
    end

    def value_is_true_or_false
      if Sail::ConstantCollection::STRING_BOOLEANS.exclude?(value)
        errors.add(:not_a_boolean_error,
                   "Boolean settings only take values inside #{Sail::ConstantCollection::STRING_BOOLEANS}")
      end
    end