Fix a bug when a document has an empty body

Add check on content length for an empty file

lib/remote_storage/riak.rb

@@ -68,7 +68,10 @@ module RemoteStorage
       when "application/json"
         return object.data.to_json
       else
-        return serializer_for(object.content_type) ? object.data : object.raw_data
+        data = serializer_for(object.content_type) ? object.data : object.raw_data
+
+        # Never return nil, always turn data into a string
+        return data.nil? ? '' : data
       end
     rescue ::Riak::HTTPFailedRequest
       server.halt 404

spec/riak_spec.rb

@@ -76,6 +76,7 @@ describe "App with Riak backend" do
       it "returns an empty body" do
         last_response.status.must_equal 200
         last_response.body.must_equal ""
+        last_response.headers["Content-Length"].must_equal '0'
       end
     end
   end