opencv FLANN with ORB descriptors?

I am trying to use FLANN with ORB descriptors, but opencv crashes with this simple code: ``` vector<vector<KeyPoint> > dbKeypoints; vector<Mat> dbDescriptors; vector<Mat> objects; /* load Descriptors from images (with OrbDescriptorExtractor()) */ FlannBasedMatcher matcher; matcher.add(dbDescriptors); matcher.train() //> Crash! ``` If I use `SurfDescriptorExtractor()` it works well. How can I solve this? OpenCV says: ``` OpenCV Error: Unsupported format or combination of formats (type=0 ) in unknown function, file D:\Value\Personal\Parthenope\OpenCV\modules\flann\sr c\miniflann.cpp, line 299 ```