InRange not show error

var m = arg.Mat;
var lower_blue = new OpenCvSharp.Scalar(20, 100, 100);
ar upper_blue = new OpenCvSharp.Scalar(30, 255, 255);
Cv2.InRange(m, lower_blue, upper_blue, mask);
Cv2.ImShow("a", mask);
/// App in Mobile stop working but not show error.
help me pls.