puyopuyotetr.is/db/migrate/20180310000000_change_columns_in_notifications_nonnullable.rb

class ChangeColumnsInNotificationsNonnullable < ActiveRecord::Migration[5.1]
  def change
    safety_assured do
      change_column_null :notifications, :activity_id, false
      change_column_null :notifications, :activity_type, false
      change_column_null :notifications, :account_id, false
      change_column_null :notifications, :from_account_id, false
    end
  end
end