fix: checking if hp_list is populated

Author: ismasou

src/framework/HardProcess.cc

@@ -123,9 +123,12 @@ void HardProcess::CollectHeader(weak_ptr<JetScapeWriter> w) {
     header.SetSigmaErr(GetSigmaErr());
     header.SetPtHat(GetPtHat());
     header.SetEventWeight(GetEventWeight());
-    header.SetVertexX(hp_list[0]->x_in().x());
-    header.SetVertexY(hp_list[0]->x_in().y());
-    header.SetVertexZ(hp_list[0]->x_in().z());
+
+    if (hp_list.size() > 0) {
+      header.SetVertexX(hp_list[0]->x_in().x());
+      header.SetVertexY(hp_list[0]->x_in().y());
+      header.SetVertexZ(hp_list[0]->x_in().z());
+    }
   }
 }