add reproducer and bugfix

modules/objdetect/src/hog.cpp

@@ -122,6 +122,12 @@ void HOGDescriptor::setSVMDetector(InputArray _svmDetector)
     _svmDetector.getMat().convertTo(svmDetector, CV_32F);
     CV_Assert(checkDetectorSize());
 
+    if (_svmDetector.empty())
+    {
+        oclSvmDetector = UMat();
+        return;
+    }
+
     Mat detector_reordered(1, (int)svmDetector.size(), CV_32FC1);
 
     size_t block_hist_size = getBlockHistogramSize(blockSize, cellSize, nbins);

modules/objdetect/test/opencl/test_hogdetector.cpp

@@ -93,6 +93,25 @@ OCL_TEST_P(HOG, GetDescriptors)
     EXPECT_MAT_SIMILAR(cpu_desc, gpu_desc, 1e-1);
 }
 
+OCL_TEST_P(HOG, SVMDetector)
+{
+    HOGDescriptor hog_first, hog_second;
+
+    // empty -> empty
+    hog_first.copyTo(hog_second);
+
+    // first -> both
+    hog_first.setSVMDetector(hog_first.getDefaultPeopleDetector());
+    hog_first.copyTo(hog_second);
+
+    // both -> both
+    hog_first.copyTo(hog_second);
+
+    // second -> empty
+    hog_first.setSVMDetector(cv::noArray());
+    hog_first.copyTo(hog_second);
+}
+
 OCL_TEST_P(HOG, Detect)
 {
     HOGDescriptor hog;