Handle non-existing as well as zero-length summary lists.

1 files changed, 1 insertions, 1 deletions

diff --git a/rules.js b/rules.js
index 771cbe1..0521b80 100644
--- a/rules.js
+++ b/rules.js
@@ -315,7 +315,7 @@ function print_plain_summary(verb, list) {
 }
 
 function print_summary(summary, verb) {
-	if (summary.length > 0) {
+	if (summary && summary.length > 0) {
 		log(verb)
 		map_for_each(summary, (s, list) => {
 			log(">%" + s + "\n" + make_summary(list))