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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def add_unique_identity(session, uuid):
 """Add a unique identity to the session. This function adds a unique identity to the session with `uuid` string as unique identifier. This identifier cannot be empty or `None`. When the unique identity is added, a new empty profile for this object is created too. As a result, the function returns a new `UniqueIdentity` object. :param session: database session :param uuid: unique identifier for the unique identity :return: a new unique identity :raises ValueError: when `uuid` is `None` or an empty string """

    if uuid is None:
        raise ValueError("'uuid' cannot be None")
    if uuid == '':
        raise ValueError("'uuid' cannot be an empty string")

    uidentity = UniqueIdentity(uuid=uuid)
    uidentity.profile = Profile()
    uidentity.last_modified = datetime.datetime.utcnow()

    session.add(uidentity)

    return uidentity