Deal with NULL fields in mkpwent.

Modules/pwdmodule.c

@@ -44,6 +44,17 @@ exception is raised if the entry asked for cannot be found.");
       
 static PyTypeObject StructPwdType;
 
+static void
+sets(PyObject *v, int i, char* val)
+{
+  if (val)
+	  PyStructSequence_SET_ITEM(v, i, PyString_FromString(val));
+  else {
+	  PyStructSequence_SET_ITEM(v, i, Py_None);
+	  Py_INCREF(Py_None);
+  }
+}
+
 static PyObject *
 mkpwent(struct passwd *p)
 {
@@ -53,7 +64,7 @@ mkpwent(struct passwd *p)
 		return NULL;
 
 #define SETI(i,val) PyStructSequence_SET_ITEM(v, i, PyInt_FromLong((long) val))
-#define SETS(i,val) PyStructSequence_SET_ITEM(v, i, PyString_FromString(val))
+#define SETS(i,val) sets(v, i, val)
 
 	SETS(setIndex++, p->pw_name);
 	SETS(setIndex++, p->pw_passwd);