Fix bug in weight filling (#14461)

Author: jgrosseo

Framework/Core/src/StepTHn.cxx

@@ -441,15 +441,15 @@ void StepTHn::Fill(int iStep, int nParams, double positionAndWeight[])
   if (weight != 1.) {
     // initialize with already filled entries (which have been filled with weight == 1), in this case mSumw2 := mValues
     if (!mSumw2[iStep]) {
-      mSumw2[iStep] = createArray();
+      mSumw2[iStep] = createArray(mValues[iStep]);
       LOGF(info, "Created sumw2 container for step %d", iStep);
     }
   }
 
   // TODO probably slow; add StepTHnT::add ?
   mValues[iStep]->SetAt(mValues[iStep]->GetAt(bin) + weight, bin);
   if (mSumw2[iStep]) {
-    mSumw2[iStep]->SetAt(mSumw2[iStep]->GetAt(bin) + weight, bin);
+    mSumw2[iStep]->SetAt(mSumw2[iStep]->GetAt(bin) + weight * weight, bin);
   }
 }