[kaltura] Improve uploader_id extraction

youtube_dl/extractor/kaltura.py

@@ -319,6 +319,6 @@ class KalturaIE(InfoExtractor):
             'thumbnail': info.get('thumbnailUrl'),
             'duration': info.get('duration'),
             'timestamp': info.get('createdAt'),
-            'uploader_id': info.get('userId'),
+            'uploader_id': info.get('userId') if info.get('userId') != 'None' else None,
             'view_count': info.get('plays'),
         }