No detailed error message for group mismatch

[frankrolf]

Workshop find:

The @smallcaps group below does not contain Y.sc, and therefore is shorter than the @lowercase group.

@lowercase = [a b c d e f g h i j k l m n o p q r s t u v w x y z];
@smallcaps = [A.sc B.sc C.sc D.sc E.sc F.sc G.sc H.sc I.sc J.sc K.sc L.sc M.sc N.sc O.sc P.sc Q.sc R.sc S.sc T.sc U.sc V.sc W.sc X.sc Z.sc];


feature smcp { 	
	sub @lowercase by @smallcaps;
} smcp;

makeotf fails without detailing what the problem might be

makeotf [Note] Using features file at './features.fea'.
makeotfexe processing font <Exercise3-Regular>
Error executing command 'makeotfexe -f /var/folders/3f/10s9y5gx2h71pqsvycqdydh40000gn/T/tmpzpv5d8w5 -o /Users/shaghayeghbovand/Desktop/Document Fonts/Exercise3-Regular.otf -ff /Users/shaghayeghbovand/Desktop/Exercise 3 - simple family/Instances/Regular/features.fea -mf /var/folders/3f/10s9y5gx2h71pqsvycqdydh40000gn/T/tmpwg4k9iow -shw'
makeotf [Error] Failed to build output font file '/Users/shaghayeghbovand/Desktop/Document Fonts/Exercise3-Regular.otf'.

makeotf -v                              
makeotf.py v2.9.0 June 1 2021