Support Rack::Files::Iterator responses

lib/bullet/rack.rb

@@ -84,7 +84,7 @@ def html_request?(headers, response)
     def response_body(response)
       if response.respond_to?(:body)
         Array === response.body ? response.body.first : response.body
-      else
+      elsif response.respond_to?(:first)
         response.first
       end
     end

spec/bullet/rack_spec.rb

@@ -2,6 +2,8 @@
 
 require 'spec_helper'
 
+require 'rack/files'
+
 module Bullet
   describe Rack do
     let(:middleware) { Bullet::Rack.new app }
@@ -261,6 +263,15 @@ module Bullet
           expect(middleware.response_body(response)).to eq body_string
         end
       end
+
+      context 'when `response` is a Rack::Files::Iterator' do
+        let(:response) { instance_double(::Rack::Files::Iterator) }
+        before { allow(response).to receive(:is_a?).with(::Rack::Files::Iterator) { true } }
+
+        it 'should return nil' do
+          expect(middleware.response_body(response)).to be_nil
+        end
+      end
     end
   end
 end