Can't change user inside container (alpine-3.5)

[holms]

When trying to change user inside container - it doesn't work.

$ docker --tls exec -it 17330814aeea bash
bash-4.3# whoami
root
bash-4.3# su go
su: can't execute ',,,:/home/': No such file or directory
bash-4.3# cat /etc/passwd | grep go
go:x:1000:1000:Linux User,,,:/home/go:,,,:/home/

Where this ,,, comes from?