def preflight(self):
        origin = self.request.headers.get('Origin', '*')

        if origin is not 'null':
            origin = '*'

        self.set_header('Access-Control-Allow-Origin', origin)
        for k, v in CORS_HEADERS.items():
            self.set_header(k, v)
dataset/ETHPy150Open benoitc/gaffer/gaffer/gafferd/http_handlers/util.py/CorsHandler.preflight/operator `==` -> `is not`