Steps to Reproduce :

1. Navigate to Targets, click on Sessions and add a New Session, say Test Session.

2. Select Test session as the session and then delete it, Click outside the popup to close it.

3. Notice that Test Session is still selected as the session. Try adding a Target URL. You'll be greeted with an error.

As far as I understood, the delete method in OWTFSessionHandler deletes the session from the db but doesn't set it to the default value after deletion.

Snippet from api_handlers.py :

def delete(self, session_id=None, action=None):
        if session_id is None or \
           action is not None:
            raise tornado.web.HTTPError(400)
        try:
            self.get_component("session_db").delete_session(
                int(session_id))
        except exceptions.InvalidSessionReference:
            raise tornado.web.HTTPError(400)