Fix misleading comment

xmltest.cpp

@@ -1909,7 +1909,8 @@ int main( int argc, const char ** argv )
 
     {
 	    // No matter - before or after successfully parsing a text -
-	    // calling XMLDocument::Value() causes an assert in debug.
+	    // calling XMLDocument::Value() used to cause an assert in debug.
+	    // Null must be retured.
 	    const char* validXml = "<?xml version=\"1.0\" encoding=\"utf-8\" ?>"
 	                           "<first />"
 	                           "<second />";