I also got the same result.

Warning: No faces were detected.
I got the that result because there are no face in the input image.
x=np.random.randn(224, 300, 3)
So i used face image as an input image. x= cv2.imread("./face_img.jpg")
But I got the error as following:
RuntimeError: cuDNN error: CUDNN_STATUS_INTERNAL_ERROR