OpenCV empty flannbased descriptor matcher

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Hi, i am a newbie and i am trying to run a matching_to_many_images.cpp, but rewritten on java. Why when i create an Flannbased descriptor matcher, it is empty ? DescriptorMatcher descriptorMatcher = DescriptorMatcher.create(DescriptorMatcher.FLANNBASED); if (descriptorMatcher.empty()) { System.out.println("Can not create descriptor matcher of given types."); return; }