Normalize the `url` - from relative, create absolute URL.

    Args:
        base_url (str): Domain with ``protocol://`` string
        rel_url (str): Relative or absolute url.

    Returns:
        str/None: Normalized URL or None if `url` is blank.

def normalize_url(base_url, rel_url):
    """
    Normalize the `url` - from relative, create absolute URL.

    Args:
        base_url (str): Domain with ``protocol://`` string
        rel_url (str): Relative or absolute url.

    Returns:
        str/None: Normalized URL or None if `url` is blank.
    """
    if not rel_url:
        return None

    if not is_absolute_url(rel_url):
        rel_url = rel_url.replace("../", "/")

        if (not base_url.endswith("/")) and (not rel_url.startswith("/")):
            return base_url + "/" + rel_url.replace("../", "/")

        return base_url + rel_url.replace("../", "/")

    return rel_url