InRange not show error

[ghost]

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.

[ghost]

cv::Exception'
what(): /build/master_pack-android/opencv/modules/imgproc/src/color.cpp:9748: error: (-215) scn == 3 || scn == 4 in function void cv::cvtColor(cv::InputArray, cv::OutputArray, int, int)
02-05 03:03:46.713 F/libc ( 4019): Fatal signal 6 (SIGABRT), code -6 in tid 4041 (Threadpool work)