diff --git a/src/Utilities/StringTokenizer.cpp b/src/Utilities/StringTokenizer.cpp
index 6a37b50..d50ace3 100644
--- a/src/Utilities/StringTokenizer.cpp
+++ b/src/Utilities/StringTokenizer.cpp
@@ -221,7 +221,7 @@ namespace ColPack
 
 	  if (TokenStringLength == 0)
 	  {
-		return(NULL);
+		return string();
 	  }
 
 	  if (DelimiterStringLength == 0)