I currently get this when I try to deploy my project:

org.eclipse.persistence.exceptions.ValidationException Exception Description: The type [class java.time.DayOfWeek] for the attribute [endDay] on the entity class [class org.mxchange.jcontactsbusiness.opening_times.BusinessOpeningTimes] is not a valid type for an enumerated mapping. The attribute must be defined as a Java enum.. Please see server.log for more details.

I'm trying to fix this by writing a AttributeConverter<DayOfWeek, String>.