error using StarFeatureDetector + GridAdaptedFeatureDetector

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Hi, I'm trying to use the Star detector with GridAdaptedFeatureDetector but it doesn't work, the detector returns zero points. My code is the following:

vector<KeyPoint> kp0;
Mat framek0=imread("/home/raul/workspace/im15.png",0);
Ptr<FeatureDetector> star = new StarFeatureDetector(16,5,10,8,5);
Ptr<FeatureDetector> detector = new GridAdaptedFeatureDetector(star,1024,16,16);
detector->detect(framek0,kp0);
cout<<kp0.size()<<endl;

The output is a: 0.

There are no problems using only the StarFeatureDetector, it gets about 400 points in the same image.

I also tried with Ptr<featuredetector> detector = FeatureDetector::create("GridSTAR") but it does the same. GridAdaptedFeatureDetector works well when I use FAST, can someone explain me what am I doing wrong?

Thanks, Raúl