Exception on /admin/airflow/clear

[Cyril Scetbon]

Hi,

When I try to clear the past of a task I get a Oops. Here is the output I get : 
http://pastebin.com/yTYsekyB

I'm using Airflow 1.7.0 and my dag contains a SubDagOperator with a subdag 
containing a BashOperator

Is it a known issue ?

Thanks