Can't call RepresentationUsingType to create a Png

I'm trying save some byte data/image out as a Png like this....
var imageRep = NSBitmapImageRep.ImageRepFromData(image.AsTiff());
var data = imageRep.RepresentationUsingType(NSBitmapImageFileType.Png, null);

The RepresentationUsingType method isn't available.

Looking on GitHub I see this:
[Export ("representationUsingType:properties:")]
NSData RepresentationUsingTypeProperties(NSBitmapImageFileType storageType, [NullAllowed] NSDictionary properties);

is that sig correct?

I'm just starting out with macOS, is there another method I should be using? Just need to get a png in the end.