Handle empty response body on update queries

Update responses are implementation defined; some servers return an
empty body and no content type. This handles that case.

(cherry picked from commit 6a7ebef)

Author: Tom Johnson

lib/sparql/client.rb

@@ -360,6 +360,8 @@ def response(query, options = {})
     # @return [Object]
     def parse_response(response, options = {})
       case options[:content_type] || response.content_type
+        when NilClass
+          response.body
         when RESULT_BOOL # Sesame-specific
           response.body == 'true'
         when RESULT_JSON

spec/client_spec.rb

@@ -25,7 +25,7 @@
 
     def response(header)
       response = Net::HTTPSuccess.new '1.1', 200, 'body'
-      response.content_type = header
+      response.content_type = header if header
       allow(response).to receive(:body).and_return('body')
       response
     end
@@ -95,10 +95,9 @@ def response(header)
       subject.query(query, :content_type => SPARQL::Client::RESULT_JSON)
     end
 
-    it "should handle successful response with overridden JSON header" do
-      expect(subject).to receive(:request).and_yield response(SPARQL::Client::RESULT_JSON)
-      expect(subject.class).to receive(:parse_xml_bindings)
-      subject.query(query, :content_type => SPARQL::Client::RESULT_XML)
+    it "should handle successful response with no content type" do
+      expect(subject).to receive(:request).and_yield response(nil)
+      expect { subject.query(query) }.not_to raise_error
     end
 
     it "should handle successful response with overridden plain header" do