Fix XML deprecation

diff --git a/src/Util/XML.php b/src/Util/XML.php
index e5fa4009f3dcf23936715ec0d1aea6b36bcf83b9..c35f19b8a8e584619b4b14ca9ea8349c09d1da0e 100644 (file)
--- a/src/Util/XML.php
+++ b/src/Util/XML.php
@@ -118,7 +118,7 @@ class XML
                                                $namespace = null;
                                        }
 
-                                       $element->addAttribute($attr_key, $attr_value, $namespace);
+                                       $element->addAttribute($attr_key, $attr_value ?? '', $namespace);
                                }
 
                                continue;