you can just put one value in the Enum and then, set the empty value as the other value,
this way, the dropdown will show only two values always.
Hope it helps!
If you could, share more information about your database and/or the source of the data view.
But I guess that you did commit an object with a null field. Check the built-in database.
If you want to remove the empty value from UI, then you can refer this question