RSpec - Undefined method `key?'

I'm trying to run a test for rendering templates and ran into the error:

undefined method `key?' for 1014:Fixnum

The stub of my model's instance works as it should in my route tests but not so much here. What am I doing wrong?

describe RestaurantsController do
  let(:restaurant) { FactoryGirl.build_stubbed(:restaurant) }

  describe 'GET #show' do
    before { get :show, restaurant.id }

    it { should render_template('show') }
  end
end

Full Error

 1) RestaurantsController GET #show 
     Failure/Error: before { get :show, restaurant.id }
     NoMethodError:
       undefined method `key?' for 1014:Fixnum
     # /Library/Ruby/Gems/2.0.0/gems/actionpack-4.2.0/lib/action_controller/test_case.rb:744:in `html_format?'
     # /Library/Ruby/Gems/2.0.0/gems/actionpack-4.2.0/lib/action_controller/test_case.rb:598:in `process'
     # /Library/Ruby/Gems/2.0.0/gems/actionpack-4.2.0/lib/action_controller/test_case.rb:65:in `process'
     # /Library/Ruby/Gems/2.0.0/gems/devise-3.5.1/lib/devise/test_helpers.rb:19:in `block in process'
     # /Library/Ruby/Gems/2.0.0/gems/devise-3.5.1/lib/devise/test_helpers.rb:72:in `catch'
     # /Library/Ruby/Gems/2.0.0/gems/devise-3.5.1/lib/devise/test_helpers.rb:72:in `_catch_warden'
     # /Library/Ruby/Gems/2.0.0/gems/devise-3.5.1/lib/devise/test_helpers.rb:19:in `process'
     # /Library/Ruby/Gems/2.0.0/gems/actionpack-4.2.0/lib/action_controller/test_case.rb:505:in `get'
     # ./spec/controllers/restaurants_controller_spec.rb:15:in `block (3 levels) in <top (required)>'