diff --git a/libraries/classes/Server/Privileges.php b/libraries/classes/Server/Privileges.php
index a61051ab0f..152de635bb 100644
--- a/libraries/classes/Server/Privileges.php
+++ b/libraries/classes/Server/Privileges.php
@@ -2681,8 +2681,8 @@ class Privileges
     public function mergePrivMapFromResult(array &$privMap, $result)
     {
         while ($row = $this->dbi->fetchAssoc($result)) {
-            $user = $row['User'];
-            $host = $row['Host'];
+            $user = (string) $row['User'];
+            $host = (string) $row['Host'];
             if (! isset($privMap[$user])) {
                 $privMap[$user] = [];
             }
@@ -4497,10 +4497,10 @@ class Privileges
         $dbname_is_wildcard = null;
 
         if (isset($_REQUEST['username'])) {
-            $username = $_REQUEST['username'];
+            $username = (string) $_REQUEST['username'];
         }
         if (isset($_REQUEST['hostname'])) {
-            $hostname = $_REQUEST['hostname'];
+            $hostname = (string) $_REQUEST['hostname'];
         }
         /**
          * Checks if a dropdown box has been used for selecting a database / table
diff --git a/server_privileges.php b/server_privileges.php
index bfa1313fd0..692a9f78d3 100644
--- a/server_privileges.php
+++ b/server_privileges.php
@@ -405,8 +405,8 @@ if (isset($_GET['export'])
     || (isset($_POST['submit_mult']) && $_POST['submit_mult'] == 'export')
 ) {
     list($title, $export) = $serverPrivileges->getListForExportUserDefinition(
-        isset($username) ? $username : null,
-        isset($hostname) ? $hostname : null
+        isset($username) ? $username : '',
+        isset($hostname) ? $hostname : ''
     );
 
     unset($username, $hostname, $grants, $one_grant);