--- a/Framework/Common/NullValue.cpp	Thu Jul 01 11:31:16 2021 +0200
+++ b/Framework/Common/NullValue.cpp	Thu Jul 01 14:39:27 2021 +0200
@@ -21,19 +21,24 @@
 
 #include "NullValue.h"
 
+#include "Utf8StringValue.h"
+
 #include <OrthancException.h>
 
 namespace OrthancDatabases
 {
   IValue* NullValue::Convert(ValueType target) const
   {
-    if (target == ValueType_Null)
+    switch (target)
     {
-      return new NullValue;
-    }
-    else
-    {
-      throw Orthanc::OrthancException(Orthanc::ErrorCode_ParameterOutOfRange);
+      case ValueType_Null:
+        return new NullValue;
+
+      case ValueType_Utf8String:
+        return new Utf8StringValue("(null)");
+
+      default:
+        throw Orthanc::OrthancException(Orthanc::ErrorCode_ParameterOutOfRange);
     }
   }
 }