From 865efb506a30f322c42bc3e0b6d0d01287758ad4 Mon Sep 17 00:00:00 2001
From: Andreas Suter <andreas.suter@psi.ch>
Date: Mon, 12 Apr 2021 07:50:37 +0200
Subject: [PATCH] make sure that group has indeed any elements.

---
 src/classes/PMsrHandler.cpp | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/classes/PMsrHandler.cpp b/src/classes/PMsrHandler.cpp
index 5d2a25d2..c89426a7 100644
--- a/src/classes/PMsrHandler.cpp
+++ b/src/classes/PMsrHandler.cpp
@@ -7033,6 +7033,9 @@ void PMsrHandler::MakeDetectorGroupingString(TString str, PIntVector &group, TSt
     str = "";
   }
 
+  if (group.size()==0)
+    return;
+
   UInt_t i=0, j=0;
   do {
     j = i;