Issue python#129: fix calling PyTasklet_New( NULL, ...)

Re-add the test for NULL. It got lost in change 20dad21ded9c (2.7-slp) and dae0e80f141d (3.2-slp). Update the documentation.

https://bitbucket.org/stackless-dev/stackless/issues/129
(grafted from a4dfdadc7cf547e7f589e8191b8bab2c67e34f00)

Author: Anselm Kruis

Doc/c-api/stackless.rst

@@ -10,9 +10,9 @@ Tasklets
 
 .. c:function:: PyTaskletObject *PyTasklet_New(PyTypeObject *type, PyObject *func)
 
-  Return a new tasklet object.  *type* must be derived from :c:type:`PyTasklet_Type`
-  or *NULL*.  *func* must be a callable object (normal use-case) or *NULL*, if the
-  tasklet is being used via capture().
+  Return a new tasklet object. *type* must be derived from :c:type:`PyTasklet_Type`
+  or ``NULL``. *func* must be a callable object or ``NULL`` or :c:macro:`Py_None`. If *func*
+  is ``NULL`` or :c:macro:`Py_None` you must set it later with :c:func:`PyTasklet_BindEx`.
 
 .. todo: in the case where NULL is returned and slp_ensure_linkage fails no
    exception is set, which is in contrast elsewhere in the function.

Stackless/changelog.txt

@@ -9,6 +9,9 @@ What's New in Stackless 3.X.X?
 
 *Release date: 20XX-XX-XX*
 
+- https://bitbucket.org/stackless-dev/stackless/issues/129
+  C-API: Calling PyTasklet_New( NULL, ...) no longer crashes.
+
 - https://bitbucket.org/stackless-dev/stackless/issues/128
   Fix pickling of the module 'stackless'.
 

Stackless/module/taskletobject.c

@@ -216,11 +216,14 @@ tasklet_dealloc(PyTaskletObject *t)
 PyTaskletObject *
 PyTasklet_New(PyTypeObject *type, PyObject *func)
 {
+    if (type == NULL) {
+        type = &PyTasklet_Type;
+    }
     if (!PyType_IsSubtype(type, &PyTasklet_Type)) {
         PyErr_SetNone(PyExc_TypeError);
         return NULL;
     }
-    if (func)
+    if (func && func != Py_None)
         return (PyTaskletObject*)PyObject_CallFunctionObjArgs((PyObject*)type, func, NULL);
     else
         return (PyTaskletObject*)PyObject_CallFunction((PyObject*)type, NULL);