def allowed_file(file_name_list: list) -> bool:
    """Return True if file extension of all passed file names is allowed"""
    allowed_extensions = {'png', 'jpg', 'jpeg', 'gif'}
    for file_name in file_name_list:
        if not file_name:
            return False
        if file_name.split('.')[-1].lower() not in allowed_extensions:
            return False
    return True