问javacv中的NullPointerException

EN

import java.io.File;
import com.googlecode.javacv.cpp.opencv_core.CvMat;
import com.googlecode.javacv.cpp.opencv_features2d.DescriptorExtractor;
import com.googlecode.javacv.cpp.opencv_features2d.FeatureDetector;
import com.googlecode.javacv.cpp.opencv_features2d.KeyPoint;
import static com.googlecode.javacv.cpp.opencv_highgui.cvLoadImageM;
import static com.googlecode.javacv.cpp.opencv_highgui.CV_LOAD_IMAGE_GRAYSCALE;

public class test {

static FeatureDetector featureDetector;
static DescriptorExtractor descriptorExtractor;

public static void main(String[] args) 
{
    featureDetector = FeatureDetector.create("SIFT");
    descriptorExtractor=DescriptorExtractor.create("SIFT");
    File file=new File("C:\\temp\\305.jpg");
    CvMat image= cvLoadImageM(file.getAbsolutePath(),CV_LOAD_IMAGE_GRAYSCALE);
    if(image==null)
        System.out.println("image is null");
    KeyPoint keypoints = new KeyPoint(null); 
    featureDetector.detect(image,keypoints,null);
    CvMat featurs = new CvMat(null) ; 
    descriptorExtractor.compute(image, keypoints, featurs);
    System.out.println(featurs);

}
}

featureDetector.detect(image,keypoints,null);