code: def _build_save_container(platform, registry, load_cache) -> Optional[str]:
      
      docker_tag = build_util.get_docker_tag(platform=platform, registry=registry)
  
      # Preload cache
      if load_cache:
          load_docker_cache(registry=registry, docker_tag=docker_tag)
  
      # Start building
      logging.debug('Building %s as %s', platform, docker_tag)
      try:
          # Increase the number of retries for building the cache.
          image_id = build_util.build_docker(docker_binary='docker', platform=platform, registry=registry, num_retries=10, no_cache=False)
          logging.info('Built %s as %s', docker_tag, image_id)
  
          # Push cache to registry
          _upload_image(registry=registry, docker_tag=docker_tag, image_id=image_id)
          return None
      except Exception:
          logging.exception('Unexpected exception during build of %s', docker_tag)
          return platform
docs: Build image for passed platform and upload the cache to the specified S3 bucket
      :param platform: Platform
      :param registry: Docker registry name
      :param load_cache: Load cache before building
      :return: Platform if failed, None otherwise