FIX: APPEND a word on object should set the value to NONE instead of UNSET

related to: metaeducation/rebol-issues#708

Author: Oldes

src/core/t-object.c

@@ -83,8 +83,8 @@ static void Append_Obj(REBSER *obj, REBVAL *arg)
 			if ((VAL_WORD_CANON(arg) == SYM_SELF) && !IS_SELFLESS(obj))
 				Trap0(RE_SELF_PROTECTED);
 			Expand_Frame(obj, 1, 1); // copy word table also
-			Append_Frame(obj, 0, VAL_WORD_SYM(arg));
-			// val is UNSET
+			val = Append_Frame(obj, 0, VAL_WORD_SYM(arg));
+			SET_NONE(val);
 		}
 		return;
 	}

src/tests/units/object-test.r3

@@ -39,4 +39,18 @@ Rebol [
 
 ===end-group===
 
+===start-group=== "APPEND on OBJECT"
+	;@@ https://github.com/rebol/rebol-issues/issues/708
+	--test-- "issue-708"
+		o: object []
+		append o 'x
+		--assert none? o/x
+		append o [y]
+		--assert none? o/y
+		append o [x: 1 y: 2]
+		--assert o/x = 1
+		--assert o/y = 2
+
+===end-group===
+
 ~~~end-file~~~