diff -up sudo-1.8.6p7/plugins/sudoers/match.c.segfault-null-group-list sudo-1.8.6p7/plugins/sudoers/match.c
--- sudo-1.8.6p7/plugins/sudoers/match.c.segfault-null-group-list	2016-05-11 10:22:29.201786896 +0200
+++ sudo-1.8.6p7/plugins/sudoers/match.c	2016-05-11 10:22:29.212786739 +0200
@@ -164,6 +164,9 @@ runaslist_matches(struct member_list *us
     int group_matched = UNSPEC;
     debug_decl(runaslist_matches, SUDO_DEBUG_MATCH)
 
+    if (user_list == NULL)user_list = ∅
+    if (group_list == NULL)group_list = ∅
+
     if (runas_pw != NULL) {
 	/* If no runas user or runas group listed in sudoers, use default. */
 	if (tq_empty(user_list) && tq_empty(group_list))