Issue #19437: Cleanup r_ref() of the marshal module

Python/marshal.c

@@ -827,12 +827,13 @@ r_ref_insert(PyObject *o, Py_ssize_t idx, int flag, RFILE *p)
 static PyObject *
 r_ref(PyObject *o, int flag, RFILE *p)
 {
-    if (o != NULL && flag) { /* currently only FLAG_REF is defined */
+    assert(flag & FLAG_REF);
+    if (o == NULL)
+        return NULL;
     if (PyList_Append(p->refs, o) < 0) {
         Py_DECREF(o); /* release the new object */
         return NULL;
     }
-    }
     return o;
 }