flask error RuntimeError RuntimeError: The session is unavailable because no secret key was set. Set the secret_key on the application to something unique and secret. code example

Example: The session is unavailable because no secret key was set. Set the secret_key on the application to something unique and secret.

if __name__ == "__main__":
    app.secret_key = 'super secret key'
    app.config['SESSION_TYPE'] = 'filesystem'

    sess.init_app(app)

    app.debug = True
    app.run()