private async Task <List <HandlerServiceResult> > ConfigureOperationCategory(string answer, User user)
        {
            answer = answer.Trim();

            if (string.IsNullOrEmpty(answer))
            {
                return(new List <HandlerServiceResult> {
                    _resultService.BuildEmptyAnswerErrorResult()
                });
            }

            var userCategories = await _documentServiceHelper.GetUserCategoriesByTypeAsync(user);

            var category = userCategories.FirstOrDefault(c => c.Name.Equals(answer));

            if (category == null)
            {
                return(new List <HandlerServiceResult> {
                    _resultService.BuildOperationCategoryNotFoundErrorResult()
                });
            }

            user.Context.CategoryId = category.Id;

            var operation = await GetOrCreateOperationAsync(user);

            operation.CategoryId = category.Id;

            await _documentServiceHelper.UpdateOperationAsync(operation);

            user.Context.CurrentNode = user.Context.CurrentNode.Children.FirstOrDefault();

            var nextQuestion = await _questionService.BuildQuestion(user);

            await _userDocumentService.UpdateAsync(user);

            return(new List <HandlerServiceResult> {
                nextQuestion
            });
        }