diff --git a/src/runtime/python/expr.c b/src/runtime/python/expr.c
index 3cd0666bd..b6ceff16a 100644
--- a/src/runtime/python/expr.c
+++ b/src/runtime/python/expr.c
@@ -1031,7 +1031,7 @@ ExprFun_init(ExprFunObject *self, PyObject *args, PyObject *kwds)
         return -1;
     }
     Py_INCREF(self->name);
-    if (PyList_Size(list) != 0) {
+    if (list != NULL && PyList_Size(list) != 0) {
         PyErr_SetString(PyExc_TypeError, "The list of arguments must be empty");
         return -1;
     }