Index: dba/csv.cpp
===================================================================
--- dba/csv.cpp	(revision 18300)
+++ dba/csv.cpp	(working copy)
@@ -872,7 +872,9 @@
       //std::string data(applyFilter((st_to_db)member->func,(char*)pObject + (int)(member -> offset),(Database::StoreType)member->type));
       dba::StoreableFilterBase* filter = (StoreableFilterBase*)member->func;
       setFilterPtr(*filter,(char*)pObject + (int)(member -> offset));
-      std::string data(filter->toString(mConvSpecs));
+      std::string data;
+      if (!filter->isNull())
+        data = filter->toString(mConvSpecs);
       int pos = getMappingPosByName(mMappings,current->name, member->name);
       if (pos != -1) {
         outmap[pos] = data;