Avoid calling functions with an empty string as format string

Directly pass NULL rather than an empty string.
diff --git a/Modules/_sqlite/module.c b/Modules/_sqlite/module.c
index 7cd6d2a..cc45331 100644
--- a/Modules/_sqlite/module.c
+++ b/Modules/_sqlite/module.c
@@ -192,7 +192,7 @@
     }
 
     /* convert the name to upper case */
-    name = _PyObject_CallMethodId(orig_name, &PyId_upper, "");
+    name = _PyObject_CallMethodId(orig_name, &PyId_upper, NULL);
     if (!name) {
         goto error;
     }