php warning fix

diff --git a/lib/Twig/Extension/Core.php b/lib/Twig/Extension/Core.php
index 88f545b..c0ab8cb 100644 (file)
--- a/lib/Twig/Extension/Core.php
+++ b/lib/Twig/Extension/Core.php
@@ -238,9 +238,10 @@ function twig_date_format_filter($date, $format = 'F j, Y H:i', $timezone = null
 {
     if (!$date instanceof DateTime && !$date instanceof DateInterval) {
         if (ctype_digit((string) $date)
-            || (('-' == $date[0])
-                && (ctype_digit(substr($date, 1))))
-        ) {
+               || (!empty($date[0])
+                               && ('-' === $date[0])
+                               && ctype_digit(substr($date, 1)))
+               ) {
             $date = new DateTime('@'.$date);
             $date->setTimezone(new DateTimeZone(date_default_timezone_get()));
         } else {