From b85aae160260360cd1429f92e1656bd31d937bd8 Mon Sep 17 00:00:00 2001
From: anagainaru <ana.gainaru@gmail.com>
Date: Thu, 7 Nov 2024 15:23:27 -0500
Subject: [PATCH] Default expression string for derived variables should be an
 empty string and not null

---
 source/adios2/core/Engine.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/source/adios2/core/Engine.h b/source/adios2/core/Engine.h
index 17d3c36011..c52c9a2246 100644
--- a/source/adios2/core/Engine.h
+++ b/source/adios2/core/Engine.h
@@ -509,7 +509,7 @@ class Engine
         return false;
     }
 
-    virtual std::string VariableExprStr(const VariableBase &) { return NULL; }
+    virtual std::string VariableExprStr(const VariableBase &) { return ""; }
 
     /** Notify the engine when a new attribute is defined. Called from IO.tcc
      */