diff --git a/p/C0XF2N.m b/p/C0XF2N.m
index df8b009..539ffe5 100644
--- a/p/C0XF2N.m
+++ b/p/C0XF2N.m
@@ -529,6 +529,7 @@ ADDINN(ZG,ZS,ZARY) ; ADD IF NOT NULL
  ;  FORMAT IS ZARY(PRED)=OBJ
  N ZI S ZI=""
  F  S ZI=$O(ZARY(ZI)) Q:ZI=""  D  ;
+ . ;I ZARY(ZI)="" S ZARY(ZI)="NULL"
  . I ZARY(ZI)'="" D  ;
  . . D ADD^C0XF2N(ZG,ZS,ZI,ZARY(ZI))
  . . I $D(DEBUG) W !,"ADDING",ZI," ",ZARY(ZI)