railsのNoMethodError

employees.rb
1ActiveAdmin.register Employee do
2  permit_params :name, :department, :gender, :birth, :joined_date, :payment, :note
3end

vagrant@ubuntu-bionic:/vagrant/rails+vue$ rails g controller ApiController
/var/lib/gems/2.5.0/gems/activerecord-6.0.2.1/lib/active_record/enum.rb:227:in `assert_valid_enum_definition_values': undefined method `all?' for 0:Integer (NoMethodError)
	from /var/lib/gems/2.5.0/gems/activerecord-6.0.2.1/lib/active_record/enum.rb:156:in `block in enum'
	from /var/lib/gems/2.5.0/gems/activerecord-6.0.2.1/lib/active_record/enum.rb:155:in `each'
	from /var/lib/gems/2.5.0/gems/activerecord-6.0.2.1/lib/active_record/enum.rb:155:in `enum'
	from /vagrant/rails+vue/app/models/employee.rb:4:in `<class:Employee>'
	from /vagrant/rails+vue/app/models/employee.rb:1:in `<top (required)>'
	from /var/lib/gems/2.5.0/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:22:in `require'
	from /var/lib/gems/2.5.0/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:22:in `block in require_with_bootsnap_lfi'
	from /var/lib/gems/2.5.0/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/loaded_features_index.rb:92:in `register'
	from /var/lib/gems/2.5.0/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:21:in `require_with_bootsnap_lfi'
	from /var/lib/gems/2.5.0/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:30:in `require'
	from /var/lib/gems/2.5.0/gems/zeitwerk-2.2.2/lib/zeitwerk/kernel.rb:16:in `require'
	from /vagrant/rails+vue/app/admin/employees.rb:1:in `<top (required)>'
	from /var/lib/gems/2.5.0/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:54:in `load'
	from /var/lib/gems/2.5.0/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:54:in `load'
	from /var/lib/gems/2.5.0/gems/activeadmin-2.6.0/lib/active_admin/application.rb:123:in `block in load'
	from /var/lib/gems/2.5.0/gems/activeadmin-2.6.0/lib/active_admin/error.rb:43:in `capture'
	from /var/lib/gems/2.5.0/gems/activeadmin-2.6.0/lib/active_admin/application.rb:123:in `load'
	from /var/lib/gems/2.5.0/gems/activeadmin-2.6.0/lib/active_admin/application.rb:115:in `block in load!'
	from /var/lib/gems/2.5.0/gems/activeadmin-2.6.0/lib/active_admin/application.rb:115:in `each'
	from /var/lib/gems/2.5.0/gems/activeadmin-2.6.0/lib/active_admin/application.rb:115:in `load!'
	from /var/lib/gems/2.5.0/gems/activeadmin-2.6.0/lib/active_admin/application.rb:141:in `routes'
	from /var/lib/gems/2.5.0/gems/activeadmin-2.6.0/lib/active_admin.rb:76:in `routes'
	from /vagrant/rails+vue/config/routes.rb:2:in `block in <top (required)>'
	from /var/lib/gems/2.5.0/gems/actionpack-6.0.2.1/lib/action_dispatch/routing/route_set.rb:429:in `instance_exec'
	from /var/lib/gems/2.5.0/gems/actionpack-6.0.2.1/lib/action_dispatch/routing/route_set.rb:429:in `eval_block'
	from /var/lib/gems/2.5.0/gems/actionpack-6.0.2.1/lib/action_dispatch/routing/route_set.rb:411:in `draw'
	from /vagrant/rails+vue/config/routes.rb:1:in `<top (required)>'
・・・

employee.rb
1class Employee < ApplicationRecord
2  GENDERS = { other: 0, male: 1, female: 2}
3
4  enum gender = GENDERS
5
6  validates :gender, inclusion: { in: GENDERS.key.concat(GENDERS.keys.map(&:to_s))}, exclusion: { in: [nil] }
7  validates :name, exclusion: { in: [nil, ""] }
8  validates :department, exclusion: { in: [nil] }
9  validates :payment, numericality: true, exclusion: { in: [nil] }
10  validates :note, exclusion: { in: [nil] }
11end

railsでhttps://qiita.com/tatsurou313/items/4f18c0d4d231e2fb55f4#%E3%82%A2%E3%83%97%E3%83%AA%E3%82%B1%E3%83%BC%E3%82%B7%E3%83%A7%E3%83%B3%E3%81%AE%E5%85%A8%E4%BD%93%E5%83%8Fこの記事に載っているアプリケーションを開発しています。

ActiveAdminを導入しマイグレーションをしたのですが、それ以降rails g controllerで新しいコントローラーを作ってもrails generate active_admin:resource EmployeeでモデルをActiveAdminでCRUDできるようなコマンドを打っても、bundle exec rails cを打っても画像のような同じエラーが出てしまいます。
確認をお願いします。