public async Task <ActionResult <ExerciseForReturnDto> > GetExerciseAsync(int id)
        {
            var exercise = await exerciseRepository.GetByIdAsync(id);

            if (exercise == null)
            {
                return(NotFound());
            }

            var exerciseToReturn = mapper.Map <ExerciseForReturnDto>(exercise);

            return(Ok(exerciseToReturn));
        }