document return value for PyImport_GetLazyImportsFilter

Doc/c-api/import.rst

@@ -349,7 +349,8 @@ Importing Modules
 
 .. c:function:: PyObject* PyImport_GetLazyImportsFilter()
 
-   Gets the current lazy imports filter. Returns a :term:`strong reference`.
+   Return a :term:`strong reference` to the current lazy imports filter,
+   or ``NULL`` if none exists. This function always succeeds.
 
    .. versionadded:: next
 

Python/import.c

@@ -4802,7 +4802,9 @@ PyImport_SetLazyImportsFilter(PyObject *filter)
     return 0;
 }
 
-/* Gets the lazy imports filter. Returns a new reference. */
+/* Return a strong reference to the current lazy imports filter
+ * or NULL if none exists. This function always succeeds.
+ */
 PyObject *
 PyImport_GetLazyImportsFilter(void)
 {

Python/sysmodule.c

@@ -2815,6 +2815,7 @@ sys_get_lazy_imports_filter_impl(PyObject *module)
 {
     PyObject *filter = PyImport_GetLazyImportsFilter();
     if (filter == NULL) {
+        assert(!PyErr_Occurred());
         Py_RETURN_NONE;
     }
     return filter;