Use '0' instead of NULL

src/model/export/ExportEngine.cpp

@@ -47,7 +47,7 @@ bool ExportEngine::SaveFile(std::vector<Operation>* operations)
     unsigned int month, year;
     std::map<wxString, int>::iterator it;
 
-    if (!operations) return NULL;
+    if (!operations) return 0;
 
     _accounts.clear();
     _categories.clear();

src/model/export/XMLExportEngine.cpp

@@ -159,7 +159,7 @@ bool XMLExportEngine::SaveFile(std::vector<Operation>* operations)
 	return false;
     }
 
-    rc = xmlTextWriterStartDocument(_writer, NULL, "UTF-8", NULL);
+    rc = xmlTextWriterStartDocument(_writer, 0, "UTF-8", 0);
 
     if (rc < 0) return false;