Agreed. A major red flag is the omission of generics usage on their methods. Just using List or Collection without type parameters is just dangerous and very bad advice for a novice programmer seeking enlightenment for Java 8 programming.
So about this setIfNotNull: I don't understand why this method is used in updateEntity. To me it seems the accountType property in the dto can be set with whatever is in the entity, null or not null. And of course, Java 8 has introduced the Optional class as a better way of dealing with null values, so why bother writing a workaround at all?
Yes, it's strange. I'd prefer to map a null in a DTO to an empty optional. I'd like even more to never have nulls in the dto in the first place.
Similarly, methods for mutation (compulsory, no less!) are red flag in FP.