Errors on unset environment variables are too agressive

[nhorman]

systemd version the issue has been seen with

253

Used distribution

Fedora 40

Linux kernel version used

6.9.6-200.fc40.x86_64

CPU architectures issue was seen on

x86_64

Component

systemd

Expected behaviour you didn't see

No response

Unexpected behaviour you saw

When starting a service with optional environment variables, systemd is now logging an error about this since commit f331434

Steps to reproduce the problem

1. run irqbalance service without IRQBALANCE_ARGS set

I can understand adding an information message about an unset variable, but an error seems overly aggressive. There are many programs out there that use a default value (like irqbalance) if an environment variable is unset, and its perfectly reasonable to expect that.

Additional program output to the terminal or log subsystem illustrating the issue

No response