Description of problem:
systemd doesn't depend on plymouth, but may give misleading errors if plymouth is not installed.

Version-Release number of selected component (if applicable):
systemd-219-19.el7.x86_64

How reproducible:
Always on systems where plymouth is not installed and you go to rescue.target or emergency.target

Steps to Reproduce:
1. Uninstall plymouth because you want a minimal install with no GUI, notice
   how you can "rpm -e" plymouth w/o any dependency issue
2. Boot system in rescue.target or emergency-target (or isolate to one of them)
3. execute
   journalctl -x -b -r

Actual results:
The first error message in reverse cronological order (the first you point your attention to) is
 systemd[NNN]: Failed at step EXEC spawning
- Subject: Process /bin/plymouth could not be executed
- Defined-By: systemd
...
- The process /bin/plymouth could not be executed and failed
...

Expected results:
Especially in critical situations (when you need to use rescue or emergency target) is of utmost importance not to mislead the user with false positives.
No errors should be logged if the situation is not an error: if systemd doesn't depend on plymouth, then it should not log errors related to the fact that plymouth is not installed

Additional info:
I understand I can ignore the error, but this is confusing and it happens in emergency situations when it may distract you from the real issue.