def split_users_blob(cls, users_blob):
        """
        Split the given string of users by ``,`` and whitespace.

        Returns a set.
        """
        users_blob_split = cls.users_blob_split_pattern.split(users_blob)
        if len(users_blob_split) == 0:
            return []
        if users_blob_split[0] == '':
            del users_blob_split[0]
        if len(users_blob_split) > 0 and users_blob_split[-1] == '':
            del users_blob_split[-1]
        return set(users_blob_split)