docs: def _get_request_body_bytes_only(param_name, param_value):
      '''Validates the request body passed in and converts it to bytes
      if our policy allows it.'''
      if param_value is None:
          return b''
  
      if isinstance(param_value, bytes):
          return param_value
  
      raise TypeError(_ERROR_VALUE_SHOULD_BE_BYTES.format(param_name))