After updating grape to 1.2.5 target_class options seems not working

Hello!
After we updated grape to 1.2.5 we can no longer mount grape (inside rails application),
here is minimal failing example:

# frozen_string_literal: true

module API
  module V2
    class Root < Grape::API
      get :path do
      end
    end

    class Documentation < Grape::API
      add_swagger_documentation(
        target_class: ::API::V2::Root,
      )
    end
  end
end

and here is stack trace:

8: from /.../.rvm/gems/ruby-2.6.5/gems/grape-1.2.5/lib/grape/api.rb:40:in `block (2 levels) in override_all_methods!'
7: from /.../.rvm/gems/ruby-2.6.5/gems/grape-1.2.5/lib/grape/api.rb:144:in `add_setup'
6: from /.../.rvm/gems/ruby-2.6.5/gems/grape-1.2.5/lib/grape/api.rb:144:in `each'
5: from /.../.rvm/gems/ruby-2.6.5/gems/grape-1.2.5/lib/grape/api.rb:145:in `block in add_setup'
4: from /.../.rvm/gems/ruby-2.6.5/gems/grape-1.2.5/lib/grape/api.rb:153:in `replay_step_on'
3: from /.../.rvm/gems/ruby-2.6.5/gems/grape-swagger-0.33.0/lib/grape-swagger.rb:129:in `add_swagger_documentation'
2: from /.../.rvm/gems/ruby-2.6.5/gems/grape-swagger-0.33.0/lib/grape-swagger.rb:27:in `combine_routes'
1: from /.../.rvm/gems/ruby-2.6.5/gems/grape-swagger-0.33.0/lib/grape-swagger.rb:27:in `each'
/.../.rvm/gems/ruby-2.6.5/gems/grape-swagger-0.33.0/lib/grape-swagger.rb:41:in `block in combine_routes': undefined method `unshift' for nil:NilClass (NoMethodError)

Reproduce the minimal Rails example and follow the stack trace into grape-swagger.rb, especially combine_routes around lines 27 and 41 and add_swagger_documentation around line 129. Check how target_class is passed after the grape 1.2.5 update; done means the example mounts without the nil.unshift error and the Swagger routes remain available.