def validate_tensor_fields(tensor_fields: Optional[List[str]]) -> None:
    """Validate the tensor fields
    Args:
        tensor_fields: the tensor fields
    Raises InvalidArgError if the tensor fields are invalid, and this should terminate the add_document process
    """
    if tensor_fields is None:
        raise errors.BadRequestError("tensor_fields must be explicitly provided as a list for unstructured index. "
                                     "If you don't want to vectorise any field, please provide an empty list [].")
    if "_id" in tensor_fields:
        raise errors.BadRequestError(message="`_id` field cannot be a tensor field.")
Validate the tensor fields
    Args:
        tensor_fields: the tensor fields
    Raises InvalidArgError if the tensor fields are invalid, and this should terminate the add_document process
    
src/marqo/core/unstructured_vespa_index/unstructured_validation.py