Fix untagging when Tags key is not present.

Author: Scot Kronenfeld

aws_lambda/aws_lambda.py

@@ -641,8 +641,9 @@ def update_function(
 forkey, valueincfg.get('tags').items()
  }
 iftags!=existing_cfg.get('Tags'):
-client.untag_resource(Resource=ret['FunctionArn'],
-TagKeys=list(existing_cfg['Tags'].keys()))
+ifexisting_cfg.get('Tags'):
+client.untag_resource(Resource=ret['FunctionArn'],
+TagKeys=list(existing_cfg['Tags'].keys()))
 client.tag_resource(Resource=ret['FunctionArn'], Tags=tags)