fromflaskimportFlask,send_fileapp=Flask(__name__)app.use_x_sendfile=True@app.route('/')defindex():returnsend_file('/etc/passwd',mimetype='text/plain',conditional=True)

Traceback (most recent call last):  File"/home/adrian/dev/indico/env/lib/python2.7/site-packages/flask/app.py", line1982, inwsgi_app    response=self.full_dispatch_request()  File"/home/adrian/dev/indico/env/lib/python2.7/site-packages/flask/app.py", line1614, infull_dispatch_request    rv=self.handle_user_exception(e)  File"/home/adrian/dev/indico/env/lib/python2.7/site-packages/flask/app.py", line1517, inhandle_user_exception    reraise(exc_type, exc_value, tb)  File"/home/adrian/dev/indico/env/lib/python2.7/site-packages/flask/app.py", line1612, infull_dispatch_request    rv=self.dispatch_request()  File"/home/adrian/dev/indico/env/lib/python2.7/site-packages/flask/app.py", line1598, indispatch_requestreturnself.view_functions[rule.endpoint](**req.view_args)  File"/home/adrian/dev/indico/src/flasktest.py", line10, inindexreturn send_file('/etc/passwd',mimetype='text/plain',conditional=True)  File"/home/adrian/dev/indico/env/lib/python2.7/site-packages/flask/helpers.py", line594, insend_filefile.close()AttributeError:'NoneType' object has no attribute 'close'