If auto-conversion fails, the Unicode codecs will return NULL.

This is now checked and the error passed on to the caller.

Objects/object.c

@@ -268,10 +268,11 @@ PyObject_Repr(v)
 		if (PyUnicode_Check(res)) {
 			PyObject* str;
 			str = PyUnicode_AsEncodedString(res, NULL, NULL);
-			if (str) {
 			Py_DECREF(res);
+			if (str)
 				res = str;
-			}
+			else
+				return NULL;
 		}
 		if (!PyString_Check(res)) {
 			PyErr_Format(PyExc_TypeError,
@@ -313,10 +314,11 @@ PyObject_Str(v)
 	if (PyUnicode_Check(res)) {
 		PyObject* str;
 		str = PyUnicode_AsEncodedString(res, NULL, NULL);
-        if (str) {
 		Py_DECREF(res);
+		if (str)
 			res = str;
-        }
+		else
+		    	return NULL;
 	}
 	if (!PyString_Check(res)) {
 		PyErr_Format(PyExc_TypeError,