Properly handle privatekey_pass set to null-value

lib/SimpleSAML/Utils/Crypto.php

@@ -222,12 +222,9 @@ class Crypto
 
         $ret = [
             'PEM' => $data,
+            'password' => $metadata->getString($prefix . 'privatekey_pass', null),
         ];
 
-        if ($metadata->hasValue($prefix . 'privatekey_pass')) {
-            $ret['password'] = $metadata->getString($prefix . 'privatekey_pass');
-        }
-
         return $ret;
     }