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Although Mr. Pavlenko was clear and has answered the question, I want to add something, namely using this code:

FeatureDetector fd = FeatureDetector.create(FeatureDetector.FAST);
...
fd.detect(myImageList,myImageKeyPointList);

If myImageKeyPointList is empty also an exception is raised (i guess that is the same reason as Mr. Pavlenko mentioned in his post):

Exception in thread "main" java.lang.IllegalArgumentException: Incomatible Mat
    at org.opencv.core.MatOfKeyPoint.<init>(MatOfKeyPoint.java:31)
    at org.opencv.utils.Converters.Mat_to_vector_vector_KeyPoint(Converters.java:591)
    at org.opencv.features2d.FeatureDetector.detect(FeatureDetector.java:229)
    ...

Besides i am using openCV 2.4.5 and java.