perl -E '
  no autovivification;
  my @ary; 
  push @ary, exists(&nonesuch);
  say scalar(@ary)
'
# RESULT: 0

perl -E '
  no autovivification;
  my @ary; 
  push @ary, [ exists(&nonesuch) ];
  say scalar(@ary)
'
# RESULT: Modification of a read-only value attempted at -e line 5