diff -ur usr/share/webapps/roundcubemail/index.php usr/share/webapps/roundcubemail/index.php
--- usr/share/webapps/roundcubemail/index.php	2015-09-13 22:04:42.000000000 +0300
+++ usr/share/webapps/roundcubemail/index.php	2016-01-02 17:57:29.084642755 +0200
@@ -40,7 +40,7 @@
 require_once 'program/include/iniset.php';
 
 // init application, start session, init output class, etc.
-$RCMAIL = rcmail::get_instance($GLOBALS['env']);
+$RCMAIL = rcmail::get_instance(0, $GLOBALS['env']);
 
 // Make the whole PHP output non-cacheable (#1487797)
 $RCMAIL->output->nocacheing_headers();
diff -ur usr/share/webapps/roundcubemail/program/include/rcmail.php usr/share/webapps/roundcubemail/program/include/rcmail.php
--- usr/share/webapps/roundcubemail/program/include/rcmail.php	2015-09-13 22:04:43.000000000 +0300
+++ usr/share/webapps/roundcubemail/program/include/rcmail.php	2016-01-02 17:57:21.774644403 +0200
@@ -69,7 +69,7 @@
      *
      * @return rcmail The one and only instance
      */
-    static function get_instance($env = '')
+    static function get_instance($mode = 0, $env = '')
     {
         if (!self::$instance || !is_a(self::$instance, 'rcmail')) {
             self::$instance = new rcmail($env);
diff -ur usr/share/webapps/roundcubemail/program/lib/Roundcube/rcube_session.php usr/share/webapps/roundcubemail/program/lib/Roundcube/rcube_session.php
--- usr/share/webapps/roundcubemail/program/lib/Roundcube/rcube_session.php	2015-09-13 22:04:43.000000000 +0300
+++ usr/share/webapps/roundcubemail/program/lib/Roundcube/rcube_session.php	2016-01-02 18:57:51.021174990 +0200
@@ -198,7 +198,7 @@
             return !empty($this->vars) ? (string) $this->vars : '';
         }
 
-        return null;
+        return '';
     }
 
 
@@ -324,7 +324,7 @@
             return !empty($this->vars) ? (string) $this->vars : '';
         }
 
-        return null;
+        return '';
     }