error with opencv threshold and findcontours [closed]

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I try to load two Images and get the matched keypoints and draw convexhull on the matched keypoints with bigger size ..any help with this error this my code:

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.widget.ImageView;

import org.opencv.android.Utils;
import org.opencv.core.Mat;
import org.opencv.core.MatOfDMatch;
import org.opencv.core.MatOfInt;
import org.opencv.core.MatOfKeyPoint;
import org.opencv.core.MatOfPoint;
import org.opencv.core.MatOfPoint2f;
import org.opencv.core.Point;
import org.opencv.core.Scalar;
import org.opencv.features2d.DMatch;
import org.opencv.features2d.DescriptorExtractor;
import org.opencv.features2d.DescriptorMatcher;
import org.opencv.features2d.FeatureDetector;
import org.opencv.features2d.Features2d;
import org.opencv.features2d.KeyPoint;
import org.opencv.highgui.Highgui;
import org.opencv.imgproc.Imgproc;
import org.opencv.utils.Converters;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import static java.lang.System.in;
import static org.opencv.core.CvType.CV_8UC1;
import static org.opencv.core.CvType.CV_8UC3;
import static org.opencv.features2d.Features2d.drawKeypoints;
import static org.opencv.highgui.Highgui.imread;
import static org.opencv.imgproc.Imgproc.THRESH_BINARY;
import static org.opencv.imgproc.Imgproc.convexHull;
import static org.opencv.imgproc.Imgproc.drawContours;
import static org.opencv.imgproc.Imgproc.findContours;
import static org.opencv.imgproc.Imgproc.threshold;

public class MainActivity extends AppCompatActivity {
    static {
        System.loadLibrary("opencv_java");
        System.loadLibrary("nonfree");
    }
    private ImageView imageView;
    private Bitmap inputImage; // make bitmap from image resource
    private Bitmap inputImage2; // make bitmap from image resource
    private FeatureDetector detector = FeatureDetector.create(FeatureDetector.SIFT);
    DescriptorExtractor extractor = DescriptorExtractor.create(DescriptorExtractor.SIFT);

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        imageView = (ImageView) this.findViewById(R.id.imageView);
        sift();
    }

    @Override
    public void onResume() {
        super.onResume();
    }

    public void sift() {
        inputImage = BitmapFactory.decodeResource(getResources(), R.drawable.test);
        inputImage2 = BitmapFactory.decodeResource(getResources(), R.drawable.shot);
        Mat rgba = new Mat();
        Mat rgba2 = new Mat();

        Utils.bitmapToMat(inputImage, rgba);
        Utils.bitmapToMat(inputImage2, rgba2);

        MatOfKeyPoint keyPoints = new MatOfKeyPoint();
        MatOfKeyPoint keypoints2 = new MatOfKeyPoint();

        Imgproc.cvtColor(rgba, rgba, Imgproc.COLOR_RGBA2GRAY);
        Imgproc.cvtColor(rgba2, rgba2, Imgproc.COLOR_RGBA2GRAY);

        detector.detect(rgba, keyPoints);
        detector.detect(rgba2, keypoints2);

        Mat descriptor1 = new Mat();
        Mat descriptor2 = new Mat();

        extractor.compute( rgba, keyPoints, descriptor1 );
        extractor.compute( rgba2, keypoints2, descriptor2 );

        MatOfDMatch matches1 =new MatOfDMatch();

        DescriptorMatcher matcher = DescriptorMatcher.create(DescriptorMatcher.BRUTEFORCE);
        matcher.match(descriptor2, descriptor1, matches1 );

        List<KeyPoint>obj=new ArrayList<>();
        List<KeyPoint>scene=new ArrayList<>();
        List<KeyPoint> filtered1=new ArrayList<KeyPoint>();
        List<KeyPoint> filtered2=new ArrayList<KeyPoint>();
        List<Point> filtered11=new ArrayList<>();
       // List<Point> filtered22=new ArrayList<>();

//        //Log.d("MainActivity","matches "+ matches1.size());
      //  List<DMatch> good_matches =new ArrayList<>();

        for (int i=0;i<matches1.toArray().length ;i++) {
            if (matches1.toArray()[i].distance <= 150 ) {
               // good_matches.add(matches1.toArray()[i]);
                DMatch match = matches1.toArray()[i];
                KeyPoint x = keyPoints.toList().get(match.trainIdx);
                obj.add(x);
                filtered11.add(x.pt);
                KeyPoint y = keypoints2.toList().get(match.queryIdx);
                scene.add(y);
               // filtered22.add(y.pt);

                if (y.size > x.size) {
                    filtered1.add(x);
                  //  filtered2.add(y);
                }
            }
        }

        /*********************************/
        Mat cannyMat ...