regen/regcharclass.pl: Change to work on an empty class

Future commits will add Unicode properties for this to generate macros,
and some of them may be empty in some Unicode releases.  This just
causes such a generated macro to evaluate to 0.

1 files changed, 1 insertions, 0 deletions

diff --git a/regen/regcharclass.pl b/regen/regcharclass.pl
index ca223f98d8..f67b0f9d32 100755
--- a/regen/regcharclass.pl
+++ b/regen/regcharclass.pl
@@ -579,6 +579,7 @@ sub _combine {
 # recursively convert an optree to text with reasonably neat formatting
 sub _render {
     my ( $self, $op, $combine, $brace )= @_;
+    return 0 if ! defined $op;  # The set is empty
     if ( !ref $op ) {
         return $op;
     }