diff -up ./plugins/sudoers/match.c.seqfault-null-group-list ./plugins/sudoers/match.c
--- ./plugins/sudoers/match.c.seqfault-null-group-list	2015-10-06 14:55:38.034532644 +0200
+++ ./plugins/sudoers/match.c	2015-10-06 15:00:03.821950086 +0200
@@ -159,6 +159,9 @@ 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))