[test] check that the Stream and its interpreter are not nullptr

LidarPlugin/Testing/TestHelpers.cxx

@@ -472,6 +472,12 @@ int testLidarStream(vtkLidarStream *stream,
                     const std::string& referenceFileName,
                     bool preSend)
 {
+  if(!stream)
+  {
+    std::cout << "Stream is nullptr" << std::endl;
+    return 1;
+  }
+
   int retVal = 0;
   // get VTP file name from the reference file
   std::vector<std::string> referenceFilesList;
@@ -490,6 +496,12 @@ int testLidarStream(vtkLidarStream *stream,
 
   auto interpreter = vtkLidarPacketInterpreter::SafeDownCast(stream->GetInterpreter());
 
+  if(!interpreter)
+  {
+    std::cout << "Interpreter is nullptr" << std::endl;
+    return 1;
+  }
+
   // Case of live correction : Packet are sent a first time to save calibration
   if (preSend)
   {