service is_running does not work with exit code 4

[martinhoyer]

Error code 4:
LSB: "program or service status is unknown"
systemd: "no such unit"

I would expect service.is_running() to return False, when service is not available, while like this is causes a crash, as there is run_expect([0, 1, 3]

Would it be possible to add rc 4, at least to SystemdService?