diff -r 7b0fdc1e917a Lib/test/string_tests.py
--- a/Lib/test/string_tests.py	Sat Sep 06 22:47:02 2014 +0300
+++ b/Lib/test/string_tests.py	Wed Sep 10 10:53:18 2014 +0800
@@ -1057,6 +1057,7 @@
         self.checkequal('a b c', ' ', 'join', BadSeq2())
 
         self.checkraises(TypeError, ' ', 'join')
+        self.checkraises(TypeError, ' ', 'join', None)
         self.checkraises(TypeError, ' ', 'join', 7)
         self.checkraises(TypeError, ' ', 'join', Sequence([7, 'hello', 123L]))
         try:
diff -r 7b0fdc1e917a Objects/stringobject.c
--- a/Objects/stringobject.c	Sat Sep 06 22:47:02 2014 +0300
+++ b/Objects/stringobject.c	Wed Sep 10 10:53:18 2014 +0800
@@ -1594,7 +1594,7 @@
     Py_ssize_t i;
     PyObject *seq, *item;
 
-    seq = PySequence_Fast(orig, "");
+    seq = PySequence_Fast(orig, "can only join an iterable");
     if (seq == NULL) {
         return NULL;
     }