py: Replace mp_const_stop_iteration object with MP_OBJ_NULL.
diff --git a/py/stream.c b/py/stream.c
index 7c97ee1..a0a2c68 100644
--- a/py/stream.c
+++ b/py/stream.c
@@ -154,7 +154,7 @@
     if (sz != 0) {
         return l_in;
     }
-    return mp_const_stop_iteration;
+    return MP_OBJ_NULL;
 }
 
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_stream_read_obj, 1, 2, stream_read);