Rails admin 和 cancancan，nil:NilClass 的未定义方法“new”

Question

I've followed the guides in the cancancan wiki on how to use cancancan to authenticate admins for rails_admin. It works so far, but when I try to access the admin dashboard with an account that has admin privileges, I run into the error

NoMethodError in RailsAdmin::MainController#dashboard

undefined method 'new' for nil:NilClass

https://imgur.com/bKE5mv6

What's going on and how can I fix this?

---

ability.rb

 if user.admin?
    can :manage, :all
    can :access, :rails_admin # this line
    can :dashboard, :all # and this one
  elsif user.userrole?
    can :read, Item
    can :manage, User, :user_id=>user.id
  else
    can :read, Item
  end

---

rails_admin.rb

config.authorize_with :cancancan2

According to the rails_admin wiki

---

Specifics:

rails 5.1.5

cancancan 2.1.3

rails_admin 1.3.0

devise 4.4.3

Answer 1

rails_admin.rb

  ### Popular gems integration

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

  ## == CancanCan ==
  ## 「cancan」 ng
  ## 「cancancan」 ok
  config.authorize_with :cancancan

Answer 2

I could solve it by reinstalling the admin_rails gem, In the terminal

$ rails g rails_admin:install

then I gave him overwrite YES

Answer 3

I tried to fix it but could not, so I went for Pundit gem and It worked fine with rails admin, They also have a gem with rails admin implementation which you can use. Kudos