use Message.get_param

Co-authored-by: Serhiy Storchaka <[email protected]>

Author: tungol

Lib/xml/dom/xmlbuilder.py

@@ -249,9 +249,10 @@ def _guess_media_encoding(self, source):
         info = source.byteStream.info()
         # import email.message
         # assert isinstance(info, email.message.Message)
-        for ctp_name, ctp_value in info.get_params(()):
-            if ctp_name == 'charset':
-                return ctp_value.lower()
+        charset = info.get_param('charset')
+        if charset is not None:
+            return charset.lower()
+        return None
 
 
 class DOMInputSource(object):