def close_app() -> None:
    """Closes the FiftyOne App, if necessary.

    If no App is currently open, this method has no effect.
    """
    global _session  # pylint: disable=global-statement
    if _session is not None:
        _session.close()
        _session = None
Closes the FiftyOne App, if necessary.

    If no App is currently open, this method has no effect.
    
fiftyone/core/session/session.py