def split_tag_and_service(tagged_service):
    """
    Turns a string of a service name, possibly with a tag.

    Returns:
        * A string of the service's name
        * A string of the tag (can be None)
    """
    if ':' in tagged_service:
        service, tag = tagged_service.split(':', 1)
    else:
        service = tagged_service
        tag = None
    return service, tag
