From af6fe077dd5e8b44c81340159cdc019f2a19e4a6 Mon Sep 17 00:00:00 2001
From: Ralf Becker <RalfBecker@outdoor-training.de>
Date: Fri, 31 Mar 2017 14:05:21 +0200
Subject: [PATCH] fix Call to a member function format() on null caused by
 9810077eab5d955de1f05428cd8ea634cd21fdc0

---
 calendar/inc/class.calendar_rrule.inc.php | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/calendar/inc/class.calendar_rrule.inc.php b/calendar/inc/class.calendar_rrule.inc.php
index 0d5b21bb8a..82bf0fd9f0 100644
--- a/calendar/inc/class.calendar_rrule.inc.php
+++ b/calendar/inc/class.calendar_rrule.inc.php
@@ -535,6 +535,10 @@ class calendar_rrule implements Iterator
 	 */
 	public function valid($use_just_date=false)
 	{
+		if (!$this->enddate)
+		{
+			return true;
+		}
 		if ($use_just_date)
 		{
 			return $this->current->format('Ymd') <= $this->enddate->format('Ymd');