swig %typemap generated list typeerror

[txtoth at gmail.com]

I'm trying to map a security_context_t ** to a python list. After
calling the method that returns this type when I process the returned
list in a for loop I get:
TypeError: expected string or Unicode object, NoneType found
after processing the last list entry. Can anyone see what I'm doing
wrong? Do I need to do something else to the list to somehow terminate
it?

%typemap(argout) security_context_t ** {
       PyObject *list_security_context = PyList_New(0); // Create the
list.
       if (list_security_context) {
               security_context_t **p_p_security_context_t = arg3;
               while (*p_p_security_context_t) { // Move each string
into the list.
                       security_context_t *p_security_context_t =
*p_p_security_context_t;
                       if (PyList_Append(list_security_context,
PyString_FromString((char
*)*p_security_context_t)) < 0) {
                               fprintf(stderr, "Fail to insert item in
list.\n");
                               $result = -1;
                               break;
                       }
                       p_p_security_context_t++;
               }
       }
       else {
               fprintf(stderr, "Fail to create list.\n");
               $result = -1;
       }

       $result = SWIG_Python_AppendOutput($result,
list_security_context);

}