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: 20171216120948_change_default_score_on_episodes.rb
    path of file: ./repos/annict/db/migrate
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

class ChangeDefaultScoreOnEpisodes < ActiveRecord::Migration[5.1]
  def change
    change_column_null :episodes, :score,
    
  def change
    change_column_null :episodes, :score, true
    change_column_default :episodes, :score, nil

    remove_column :episodes, :avg_rating

    add_column :works, :score, :float
    add_index :works, :score
  end