diff -r a507882736b2 Objects/tupleobject.c
--- a/Objects/tupleobject.c	Wed Jan 25 22:33:43 2017 +0900
+++ b/Objects/tupleobject.c	Fri Feb 03 20:25:12 2017 +0900
@@ -300,6 +300,13 @@ tuplerepr(PyTupleObject *v)
                 goto error;
         }
 
+        // tuple under construction may be exposed unintentionally.
+        if (v->ob_item[i] == NULL) {
+            if (_PyUnicodeWriter_WriteASCIIString(&writer, "<NULL>", 6) < 0) {
+                goto error;
+            }
+        }
+
         if (Py_EnterRecursiveCall(" while getting the repr of a tuple"))
             goto error;
         s = PyObject_Repr(v->ob_item[i]);