OpenCV4Android - an empty image after using MorphologyEX

Question

So, I'm trying to get a BlackHat Morph image, but after applying the Morph operation, I get a blank image, and I'm not sure why.

private coid convertToBlackHat( Mat passedImage )
    {
        // Create a structuring element (SE)
    int morph_size = 2;
    Mat element = Imgproc.getStructuringElement( Imgproc.MORPH_RECT, new Size( 2*morph_size + 1, 2*morph_size+1 ), new Point( morph_size, morph_size ) );

    Mat dst = new Mat(); // result matrix
    // Apply the specified morphology operation
    Imgproc.morphologyEx( passedImage, dst, MORPH_TOPHAT, element, Point(-1,-1));   


    mBlackhatOutput = dst.clone();
}

The image is a 24-bit jpeg in 1920x1080 with circles of 100 pixels on it.