rails_adminでundefined method `new' for nil:NilClass

Question

rails_adminで管理者画面を作りました。最初は上手く行ったのですが５回目くらいのときに以下のエラーが出て困っています。原因・解決方法がわかる方は教えていただけると幸いです。https://qiita.com/mailok1212/items/8e36a5a10f19023bb0c4←参考にしたサイト

Started GET "/admin" for ::1 at 2019-11-27 17:23:30 +0900
   (19.4ms)  SELECT sqlite_version(*)
   (2.0ms)  SELECT "schema_migrations"."version" FROM "schema_migrations" ORDER BY "schema_migrations"."version" ASC
Processing by RailsAdmin::MainController#dashboard as HTML
  User Load (1.4ms)  SELECT "users".* FROM "users" WHERE "users"."id" = ? ORDER BY "users"."id" ASC LIMIT ?  [["id",
3], ["LIMIT", 1]]
  ↳ config/initializers/rails_admin.rb:7:in `block (2 levels) in <top (required)>'
Completed 500 Internal Server Error in 93ms (ActiveRecord: 7.7ms | Allocations: 9176)


NoMethodError (undefined method `new' for nil:NilClass):

（今回使用したもの）
gem 'devise'
gem 'rails_admin'
gem 'rails-i18n'
gem 'cancancan'

RailsAdmin.config do |config|

  ### Popular gems integration

  ## == Devise ==
  config.authenticate_with do
    warden.authenticate! scope: :user
  end
  config.current_user_method(&:current_user)

  ## == Cancan ==
  config.authorize_with :cancan

  ## == Pundit ==
  # config.authorize_with :pundit
  end

# frozen_string_literal: true

class Ability
  include CanCan::Ability

  def initialize(user)
    if user.try(:admin?)
      can :access, :rails_admin
      can :manage, :all
    # Define abilities for the passed in user here. For example:
    #
    #   user ||= User.new # guest user (not logged in)
    #   if user.admin?
    #     can :manage, :all
    #   else
    #     can :read, :all
    #   end
    #
    # The first argument to `can` is the action you are giving the user
    # permission to do.
    # If you pass :manage it will apply to every action. Other common actions
    # here are :read, :create, :update and :destroy.
    #
    # The second argument is the resource the user can perform the action on.
    # If you pass :all it will apply to every resource. Otherwise pass a Ruby
    # class of the resource.
    #
    # The third argument is an optional hash of conditions to further filter the
    # objects.
    # For example, here the user can only update published articles.
    #
    #   can :update, Article, :published => true
    #
    # See the wiki for details:
    # https://github.com/CanCanCommunity/cancancan/wiki/Defining-Abilities
    end
  end
end

https://qiita.com/Masahiro_T/items/130d7cda3ea5de08985eこのサイトの方法を試しましたが、you are not authorized to access this page. といわれてしまいます。

Comments

[perpouh]

>you are not authorized to access this page. といわれてしまいます。 cancancanって確か権限周りのgemだったと記憶していますが、開こうとした画面に対してログインしたユーザーの権限が無いのでは？　冒頭のエラーは既に直っていて、別の現象が発生しているように見えますがいかがでしょう？

Answer 1

１からadminとcancancanの設定をし直したらできました。原因はわかりません。すみません。