Ephemeris Error on start up

Every reboot or start up of OH I have following error in log:

2020-07-11 13:07:29.103 [ERROR] [org.openhab.core.ephemeris          ] - bundle org.openhab.core.ephemeris:2.5.0 (143)[org.openhab.ephemeris(62)] : The activate method has thrown an exception

java.lang.IllegalArgumentException: No enum constant java.time.DayOfWeek.""MONDAY

	at java.lang.Enum.valueOf(Enum.java:238) ~[?:1.8.0_252]

	at java.time.DayOfWeek.valueOf(DayOfWeek.java:109) ~[?:1.8.0_252]

	at org.eclipse.smarthome.core.ephemeris.internal.EphemerisManagerImpl.addDayset(EphemerisManagerImpl.java:330) ~[?:?]

I’m on a Rpi4 running current openhabian 2.5.6-2, but I have this since a very long time.
After a few minutes this error stops and doesn’t come up again - until I restart or reboot.

Is this something I can ignore or should this be solved?
Any help is appreciated!

Check if this helps.

I added the ephemeris.cfg and the error is gone.
Thanks a lot!