EZP-32018: Fixed empty ezdate field transformation (#1464)

* EZP-32018: Fixed empty ezdate field transformation

* EZP-32018: CS

* EZP-32018: CS

Author: Bartek

lib/ezutils/classes/eztimestamp.php

@@ -14,6 +14,12 @@ class eZTimestamp
      \return a timestamp in UTC
     */
     public static function getUtcTimestampFromLocalTimestamp( $localTimestamp ) {
+
+        if ( !$localTimestamp )
+        {
+            return null;
+        }
+
         $utcTimezone = new \DateTimeZone( 'UTC' );
         $localTimezone = new \DateTimeZone( date_default_timezone_get() );
 
@@ -28,6 +34,12 @@ public static function getUtcTimestampFromLocalTimestamp( $localTimestamp ) {
      \return a timestamp in timezone defined in php.ini
     */
     public static function getLocalTimestampFromUtcTimestamp( $utcTimestamp ) {
+
+        if ( !$utcTimestamp )
+        {
+            return null;
+        }
+
         $utcTimezone = new \DateTimeZone( 'UTC' );
         $localTimezone = new \DateTimeZone( date_default_timezone_get() );