diff --git a/lib/UESUpdateHelper.php b/lib/UESUpdateHelper.php
index 19ea1d636b988cccfaf38e15bc17c862ee486767..f741c61a0a09685877eb4e28ac98d20d8016589c 100644
--- a/lib/UESUpdateHelper.php
+++ b/lib/UESUpdateHelper.php
@@ -5,6 +5,7 @@ namespace SimpleSAML\Module\perun;
 use Exception;
 use SimpleSAML\Configuration;
 use SimpleSAML\Logger;
+use SimpleSAML\Module\perun\Exception as PerunException;
 
 class UESUpdateHelper
 {
@@ -82,15 +83,20 @@ class UESUpdateHelper
                 $attrValue = [$attrValue];
             }
 
+            if (empty($attrValue)) {
+                continue;
+            }
+
             foreach ($attrValue as $extLogin) {
+                if (empty($extLogin)) {
+                    continue;
+                }
                 $userExtSource = self::getUserExtSource($adapter, $extSourceName, $extLogin);
-
                 if ($userExtSource !== null) {
                     Logger::debug(
                         self::DEBUG_PREFIX . 'Found user ext source for combination extSourceName \''
                         . $extSourceName . '\' and extLogin \'' . $extLogin . '\''
                     );
-
                     return $userExtSource;
                 }
             }
@@ -103,7 +109,11 @@ class UESUpdateHelper
     {
         try {
             return $adapter->getUserExtSource($extSourceName, $extLogin);
-        } catch (SimpleSAML\Module\perun\Exception $ex) {
+        } catch (PerunException $ex) {
+            Logger::debug(
+                self::DEBUG_PREFIX . 'Did not find extSource for combination of parameters extSourceName: \''
+                . $extSourceName . '\', extLogin: \'' . $extLogin . '\''
+            );
             return null;
         }
     }
@@ -217,7 +227,7 @@ class UESUpdateHelper
             strpos($attributeType, self::MAP_TYPE);
     }
 
-    public static function convertToString($newValue)
+    public static function convertToString($newValue): string
     {
         if (!empty($newValue)) {
             $newValue = array_unique($newValue);