Can I annotate an ObjC method to tell the static analyzer its argument is non-nil if it returns YES?

The code I'm working with has a utility function like

@implementation Utils
+ (BOOL)isNullOrEmpty:(nullable NSString *)string {
  return (string.count > 0);
}
@end

So obviously +isNullOrEmpty: only returns YES if string is non-nil, but Xcode's static analyzer doesn't know this. Is there a way to tell the analyzer that whenever this method returns true, its argument is guaranteed to be non-nil?

I thought I saw a macro that did something like this in a WWDC video a few years back, but I don't remember what it was and I haven't found anything useful googling for it.