[HttpPatch("{talkId}")]
        public ActionResult PartiallyUpdateCourseForAuthor(int speakerId,
            int talkId,
            JsonPatchDocument<TalkUpdateDto> patchDocument)
        {
            if (!_speakerRepository.SpeakerExists(speakerId))
            {
                return NotFound();
            } 

            var talkForSpeakerFromRepo = _talkRepository.GetTalk(speakerId, talkId);

            if (talkForSpeakerFromRepo == null)
            {
                var courseDto = new TalkUpdateDto();
                patchDocument.ApplyTo(courseDto, ModelState);

                if (!TryValidateModel(courseDto))
                {
                    return ValidationProblem(ModelState);
                }

                var talkToAdd = _mapper.Map<Talk>(courseDto);
                talkToAdd.Id = talkId;

                _talkRepository.AddTalk(speakerId, talkToAdd);
                _talkRepository.Save();

                var courseToReturn = _mapper.Map<TalkDto>(talkToAdd);

                return CreatedAtRoute("GetTalkForSpeaker",
                    new { speakerId, talkId = courseToReturn.Id },
                    courseToReturn);
            }

            var talkToPatch = _mapper.Map<TalkUpdateDto>(talkForSpeakerFromRepo);
            // add validation
            // patchDocument.ApplyTo(talkToPatch, ModelState);
            patchDocument.ApplyTo(talkToPatch);
            if (!TryValidateModel(talkToPatch))
            {
                return ValidationProblem(ModelState);
            }

            _mapper.Map(talkToPatch, talkForSpeakerFromRepo);

            _talkRepository.UpdateTalk(talkForSpeakerFromRepo);

            _talkRepository.Save();

            return NoContent();
        }