Object null when using the same action controller

[HttpGet("{animalId}")]
        public async Task<IActionResult> GetById(int animalId, CancellationToken cancellationToken = default)
        {
            var animal = await _animalRepository.FindByIdAsync(animalId, cancellationToken);
            return animal != null ? Ok(_mapper.Map<AnimalDTO>(animal)) : NotFound("Unable to find the requested animal"); 
        }

return CreatedAtAction(nameof(GetById), new { Id = animal.Id }, _mapper.Map<AnimalDTO>(animal));