Use stdlib for NULL
-#ifdef __APPLE__
-// http://clc-wiki.net/wiki/C_standard_library:string.h:NULL
-// Portable C90 version: NULL ((void*)0)
-# ifndef NULL
-# define NULL 0
-# endif
-#else
-# include <libio.h> // For NULL
-#endif
+# include <stdlib.h> // For NULL
#include "dyn_types.h"
#include "dyn_dict_msg_id.h"
