def _load_configuration(conf, env_var):
    """Load default configuration settings into the given :class:`Config`
    instance and optionally try to load additional settings from the file
    pointed to by the given environmental variable.

    The environmental variable will be quietly ignored if it is not set or
    it does not point to a valid configuration file.
    """
    conf.from_object('avalon.settings')
    if env_var is None:
        return False
    return conf.from_envvar(env_var, silent=True)
