Namespaced requests with optional URL params fail with empty parameter

In short: /root returns 404 but expected to route into the get with empty type. It works only on root level requests.

class API < Grape::API
  namespace :root do
    get '/(:type)' do
      params[:type]
    end
  end
end

get '/root/some_type' # => some_type
get '/root' # => 404

Full test:

require 'spec_helper'

describe Grape::API do
  subject { Class.new(Grape::API) }

  def app
    subject
  end

  describe 'url parameters' do
    it 'routes to a route with a required named url parameter' do
      subject.namespace :root do
        get '/hello' do
          'hello'
        end

        get '/:type' do
          params[:type]
        end
      end

      get '/root/hello'
      expect(last_response.body).to eq('hello')

      get '/root/some_required_type'
      expect(last_response.body).to eq('some_required_type')
    end

    it 'routes to a route with optional parameter' do
      subject.get '/(:type)' do
        "type=#{params[:type]}"
      end

      get '/hello'
      expect(last_response.body).to eq('type=hello')

      get '/'
      expect(last_response.body).to eq('type=')
    end

    it 'routes to a namespaced route with optional parameter' do
      subject.namespace :root do
        get '/(:type)' do
          "type=#{params[:type]}"
        end
      end

      get '/root/some_type'
      expect(last_response.body).to eq('type=some_type')

      get '/root'
      expect(last_response.body).to eq('type=') # => getting "Not Found"
    end
  end
end

Start with the supplied Grape::API spec for “routes to a namespaced route with optional parameter” and run the existing test suite. Trace how namespace :root combines with the optional '/(:type)' route. Done means GET /root returns a successful response with type=, while /root/some_type still returns type=some_type.