add mac macro for NULL. fixes build on mac
+#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 "dyn_types.h"
#include "dyn_dict_msg_id.h"
