@classmethod
def get(cls, key):
    """Get the config value specified by the provided key.

        TOML config files should be stored in the config folder, and the
        environment (i.e. which file to choose) should be specified by the
        ``DQENV`` environment variable.

        :param string key: The key to retrieve the value for. Nested key should
            have its components separated by dot, such as ``owner.email``.
        :returns: The value of the key if it exists, and ``None`` otherwise.
        """
    if cls._instance is None:
        cls.init()
    parts = key.split('.')
    cfg = cls._instance
    for part in parts:
        cfg = cfg.get(part)
        if cfg is None:
            return None
    return cfg
