diff -r d6c7ab5a2065 Lib/test/string_tests.py
--- a/Lib/test/string_tests.py	Thu Sep 11 10:56:59 2014 +0300
+++ b/Lib/test/string_tests.py	Fri Sep 12 14:47:46 2014 +0800
@@ -65,14 +65,12 @@
             self.assertTrue(object is not realresult)
 
     # check that object.method(*args) raises exc
-    def checkraises(self, exc, object, methodname, *args):
-        object = self.fixtype(object)
+    def checkraises(self, exc, obj, methodname, *args):
+        obj = self.fixtype(obj)
         args = self.fixtype(args)
-        self.assertRaises(
-            exc,
-            getattr(object, methodname),
-            *args
-        )
+        with self.assertRaises(exc) as cm:
+            getattr(obj, methodname)(*args)
+        self.assertNotEqual(cm.exception.message, '')
 
     # call object.method(*args) without any checks
     def checkcall(self, object, methodname, *args):
@@ -1057,6 +1055,7 @@
         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 d6c7ab5a2065 Lib/test/test_string.py
--- a/Lib/test/test_string.py	Thu Sep 11 10:56:59 2014 +0300
+++ b/Lib/test/test_string.py	Fri Sep 12 14:47:46 2014 +0800
@@ -16,13 +16,10 @@
             realresult
         )
 
-    def checkraises(self, exc, object, methodname, *args):
-        self.assertRaises(
-            exc,
-            getattr(string, methodname),
-            object,
-            *args
-        )
+    def checkraises(self, exc, obj, methodname, *args):
+        with self.assertRaises(exc) as cm:
+            getattr(string, methodname)(obj, *args)
+        self.assertNotEqual(cm.exception.message, '')
 
     def checkcall(self, object, methodname, *args):
         getattr(string, methodname)(object, *args)
diff -r d6c7ab5a2065 Lib/test/test_userstring.py
--- a/Lib/test/test_userstring.py	Thu Sep 11 10:56:59 2014 +0300
+++ b/Lib/test/test_userstring.py	Fri Sep 12 14:47:46 2014 +0800
@@ -28,14 +28,12 @@
             realresult
         )
 
-    def checkraises(self, exc, object, methodname, *args):
-        object = self.fixtype(object)
+    def checkraises(self, exc, obj, methodname, *args):
+        obj = self.fixtype(obj)
         # we don't fix the arguments, because UserString can't cope with it
-        self.assertRaises(
-            exc,
-            getattr(object, methodname),
-            *args
-        )
+        with self.assertRaises(exc) as cm:
+            getattr(obj, methodname)(*args)
+        self.assertNotEqual(cm.exception.message, '')
 
     def checkcall(self, object, methodname, *args):
         object = self.fixtype(object)
diff -r d6c7ab5a2065 Objects/stringobject.c
--- a/Objects/stringobject.c	Thu Sep 11 10:56:59 2014 +0300
+++ b/Objects/stringobject.c	Fri Sep 12 14:47:46 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;
     }