code: def _validate_name(name):
      
      if name is None:
          return
  
      # The first and las characters must be alphanumeric.
      if not all([name[0].isalnum(), name[-1].isalnum()]):
          raise ValueError("Bucket names must start and end with a number or letter.")
      return name
docs: Pre-flight ``Bucket`` name validation.
  
      :type name: str or :data:`NoneType`
      :param name: Proposed bucket name.
  
      :rtype: str or :data:`NoneType`
      :returns: ``name`` if valid.