Update/Set Result Details content of RQM Test Result Resource using OSLC/REST API

I'm trying to update a RQM Test Result resource with extendedproperty 'richTextSection' using OSLC API call to 'updateResource'. I believe 'richTextSection' is associated with Result Details section of Test Result where i want to update some content.

Even after client.updateResource executed without any exception Result Details content is not updated and missing from Test Result.

I wonder, Is this correct way to update Test Result resource? Are reportable REST APIs more convenient to achieve this update.

E.g Source code snapshot

TestResult testResult= client.getResource(testresultLocation, OSLCConstants.CT_RDF).getEntity(TestResult.class);
 Map<QName, Object> extProp1 = testResult.getExtendedProperties();
 extProp1.put(qName, "Comment updated by using API ");
 testResult.setExtendedProperties(extProp1);
 ClientResponse updateResponse = client.updateResource(testresultLocation, testResult,
                            OslcMediaType.APPLICATION_RDF_XML);

Your feedback is appreciated! Thank You!

-Jay