Description:
When "unix+admin://" is present in the configuration it uses the default path of '/run/soju/admin'. Note that "unix+admin://" is present in the default configuration thus causing the issue out of the box!

Currently this path isn't instantiated by the tmpfiles.conf configuration file, _where it probably should_.
Alternative solutions could be:
1) Shipping a different path in the default config file
2) Changing the default path in the Makefile

Here's the excerpt from soju's manual: (https://soju.im/doc/soju.1.html)
"""
•unix+admin://[path] listens on a Unix domain socket for administrative connections, such as sojuctl (default path: /run/soju/admin)
"""

Steps to reproduce:
"systemctl start soju.service" with the default config leads to failure with non-zero exit code.