Mobility: Invalid single-table inheritance type issue

first.rb

#app/models/member/first.rb

class Member::First < Member
end

Gemfile

source 'https://rubygems.org'

git_source(:github) do |repo_name|
  repo_name = "#{repo_name}/#{repo_name}" unless repo_name.include?("/")
  "https://github.com/#{repo_name}.git"
end


gem 'rails', '~> 5.0.2'
gem 'pg', '~> 0.18'
gem 'mobility', '~> 0.1.16'

group :development do
  gem 'listen', '~> 3.0.5'
end

i18n.rb

#config/initializers/i18n.rb

Rails.application.config.i18n.available_locales = %i[en fi]
Rails.application.config.i18n.default_locale = 'en'

member.rb

#app/models/member.rb

class Member < ApplicationRecord
  include Mobility
  translates :name, type: :string
end

mobility.rb

#config/initializers/mobility.rb

Mobility.configure do |config|
  config.default_backend = :column
end

rails_console.rb

#Run in rails console

-> Member.create!(type: Member::First.name)
ActiveRecord::SubclassNotFound: Invalid single-table inheritance type: Member::First is not a subclass of Member

schema.rb

ActiveRecord::Schema.define(version: 20170615120021) do
  create_table "members", force: :cascade do |t|
    t.string "type"
    t.string "name_en"
    t.string "name_fi"
  end
end

second.rb

#app/models/member/second.rb

class Member::Second < Member
end