def parse_redis_url() -> str | None:
    """Parse the REDIS_URL in config if applicable.

    Returns:
        If url is non-empty, return the URL as it is.

    Raises:
        ValueError: If the REDIS_URL is not a supported scheme.
    """
    config = get_config()
    if not config.redis_url:
        return None
    if not config.redis_url.startswith(("redis://", "rediss://", "unix://")):
        msg = "REDIS_URL must start with 'redis://', 'rediss://', or 'unix://'."
        raise ValueError(msg)
    return config.redis_url
Parse the REDIS_URL in config if applicable.

    Returns:
        If url is non-empty, return the URL as it is.

    Raises:
        ValueError: If the REDIS_URL is not a supported scheme.
    
reflex/utils/prerequisites.py