Nullable is different than empty. Consider a contrived example where I’ve extended a user table to include a new column “fullName”. By making this a nullable column, I can determine that a user has not set this value. But maybe the user sets it to an empty string. The API might want to know this and handle it differently — prompting for a value if it’s null, but ignoring “” as “this is what the user wanted to set”.
Without nullable values, I would have to create bit values in a lot of tables indicating if the value was ever set.
Another example is time stamps. Databases have timestamps for createdAt and updatedAt often. There are people who set updatedAt when they set createdAt, but there are people who don’t. I’m in the later camp. If an object was created but never updated, I want to be able to know that. How would I do this if the updatedAt column is not nullable? I’d either have to set a bit field that it has been updated, which feels suboptimal, or I could set it to something like “time.Empty{}”, which is a magic number tied to the programming language? There are plenty of other solutions here, sure, but what’s wrong with nullable fields?