diff --git a/system/src/Grav/Common/TwigExtension.php b/system/src/Grav/Common/TwigExtension.php
index f25696948..22ea46a7f 100644
--- a/system/src/Grav/Common/TwigExtension.php
+++ b/system/src/Grav/Common/TwigExtension.php
@@ -231,6 +231,10 @@ class TwigExtension extends \Twig_Extension
     {
         $output = [];
 
+        if (!$input) {
+            return $output;
+        }
+
         foreach ($input as $key => $row) {
             $output[$key] = $row[$filter];
         }