Browser Automation Field 'sessionName' must not be null.

Hello Everyone, 

I am using the package Browser Automation , 

I create a child bot using the variable type session for output; But when I call the child bot  in parent bot and trying to use the session output in other browser action . I have the following message Field 'sessionName' must not be null.

The child bot run succesfully but I think the session output is not well return even the session Id is not null