"Reflush tree false" Error message after pressing F5 when using deepsleep

[SensorsIot]

I use an example with deepsleep. F5 works as long as I comment "m.deepsleep(sleep_ms = 3000)". When it is active I get the following error message after pressing F5

os.listdir('.')
Traceback (most recent call last):
File "", line 1, in
NameError: name 'os' isn't defined

reflush tree false