nonExist now does the expected thing

lib/src/prelude/Predef.gf

@@ -36,6 +36,6 @@ resource Predef = {
   oper toStr  : (L : Type) -> L -> Str = variants {} ; -- find the "first" string
   oper mapStr : (L : Type) -> (Str -> Str) -> L -> L = variants {} ; 
                -- map all strings in a data structure; experimental ---
+  oper nonExist : Str = variants {} ;  -- a placeholder for non-existant morphological forms
 
 } ;
-

lib/src/prelude/Prelude.gf

@@ -35,7 +35,7 @@ oper
 
 -- Missing form.
 
-  nonExist : Str = variants {} ;
+  nonExist : Str = Predef.nonExist;
 
 -- Optional string with preference on the string vs. empty.