ANImage.m does not compile on OS X

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In ANImage.m in the method - (void)imageAtSize:(CGSize)size completion:(ANImageCompletion)completion {, the line id image = [self.imageAtSize objectForKey:[NSValue valueWithCGSize:size]];, does not compile on OS X. I got it to compile by changing [NSValue valueWithCGSize:size] to [NSValue valueWithSize:size].