Select filter is not working

[kot-begemot]

Spec:

activeadmin (1.4.3)
activeadmin-mongoid (0.8.0)
 remote: https://github.com/activeadmin/activeadmin-mongoid.git
 revision: ff45b6379cec574e687548b607cad225fd2cf403
 branch: master
 ransack-mongoid (0.1.0)
 remote: https://github.com/activerecord-hackery/ransack-mongoid.git
 revision: bd1935293d2f285fa7cf33d2c5c90d981bf67338

Error
undefined method +' for nil:NilClass`

Reported line
activeadmin (1.4.3) lib/active_admin/inputs/filters/select_input.rb

Active admin setup:

ActiveAdmin.register SellOrder do
 actions :all, :except => [:new, :edit, :destroy]

 index do
 selectable_column
 column :name
 column :user
 column "Domains" do |sell_order|
 sell_order.domains.count
 end
 column :state
 actions
 end

 filter :name
 filter :state, as: :select, collection: SellOrder.state_machine.states.map(&:name)
 filter :created_at

 show do
 ...
 end
end

Investigation
activeadmin-mongoid substitutes method searchable_method_name with broken equivalent, while original method itself works like a charm

[grzegorz-jakubiak]

Would you be willing to submit a PR?

[kot-begemot]

Sure, I'll do

[grzegorz-jakubiak]

@kot-begemot please try this #143