5218 posix definition of NULL
correct unistd.h and iso/stddef_iso.h
update gate source affected

@@ -896,11 +896,11 @@
                         *ptr++ = *r++;
                 }
         } else if (req->file_list)
                 strlcpy(buf, *req->file_list, sizeof (buf));
         
-        if (*buf == NULL || !strncmp(buf, SPOOLDIR, sizeof(SPOOLDIR)-1))
+        if (*buf == '\0' || !strncmp(buf, SPOOLDIR, sizeof(SPOOLDIR)-1))
                 strcpy(buf, "<File name not available>");
 
         if (strlen(buf) > (size_t) 24) {
                 char *r;