Returns a configuration variable's value or None if it is unset.

def get_config(k: str) -> Any:
    """
    Returns a configuration variable's value or None if it is unset.
    """
    # If the config has been set explicitly, use it.
    if k in list(CONFIG.keys()):
        return CONFIG[k]

    # If there is a specific PULUMI_CONFIG_<k> environment variable, use it.
    env_key = get_config_env_key(k)
    if env_key in os.environ:
        return os.environ[env_key]

    # If the config hasn't been set, but there is a process-wide PULUMI_CONFIG environment variable, use it.
    env_dict = get_config_env()
    if env_dict is not None and k in list(env_dict.keys()):
        return env_dict[k]

    return None