FK relationship configuration in EF Core that I want to be nullable. If I set the type of ClientId to be nullable (which is a custom class that wraps up a Guid value which the entire codebase uses), EF Core will complain about:Identifier to its default constant value when not set, which is causing this issue. I don't know how to instruct it not to do that.Identifier? class so using Guid? instead is not an ideal option. Using IsRequired(false) instead of Nullable<> also brought no results. I have also tried this converter: