In Oracle there is no difference between a NULL and an empty string. My understanding is that this design decision was made long long ago before there were any

In Oracle there is no difference between a NULL and an empty string. My understanding is that this design decision was made long long ago before there were any standards or a realization that this was a bad thing and now it is too late to change. By far and away, the way NULLs are handled in Oracle is the biggest problem with moving to a different database.