docs: def _renderBlockDevice(self, block_device, build):
          """Render all of the block device's values."""
          rendered_block_device = yield build.render(block_device)
          if rendered_block_device['volume_size'] is None:
              source_type = rendered_block_device['source_type']
              source_uuid = rendered_block_device['uuid']
              volume_size = self._determineVolumeSize(source_type, source_uuid)
              rendered_block_device['volume_size'] = volume_size
          return rendered_block_device