Can't get into headless pi, password not 'raspberry'

I am trying to set up a new, headless Pi 4B.  I have copied the 'lite'
image to a USB drive and created the empty 'ssh' file in the boot
partition. 

It boots OK and the ssh deamon is running but the default username
'pi' and password 'raspberry' don't work. How on earth do I get into
it to start it up?

I can edit files on the USB drive OK so I can add and modify entries
in /etc/passwd and /etc/shadow. So all I actually need to do is set it
up so the user 'pi' has no password but I'm not doing too well at
doing that at the moment.

Any ideas, or other ways to get into it?

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Chris Green
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