Convert Frame to BufferedImage using JavaCV

Question

so I have a Frame from a video:

FFmpegFrameGrabber grabber = new FFmpegFrameGrabber(videoFilePath);
grabber.start();

grabber.setFrameNumber(frameNumber);
Frame frame = grabber.grab();

and I want to convert it to a BufferedImage so currently I am using this:

Java2DFrameConverter c = new Java2DFrameConverter();
BufferedImage image = c.convert(frame);

But when I am trying to save the .png file like that

ImageIO.write(image, "png", outputFrameFile);

But I am getting the error "image == null" idk why

I tried to look for answers but nothing helped.