What is the value of an empty cell in a SQLite DB in iOS

Given a SQLite database with records consisting of multiple text columns, what is the value of an empty cell (i.e., a cell that has never been updated)? Would it be nil, 0, or possibly empty string?

For example, consider the following table where A, B, and C are text columns:

id A B C
_  _ _ _
1  d e f
2  g h
3  i

What would be the value of cells 2C, 3B, and 3C?

If I were to update this table one record at a time, using the following query

update table set A=? B=? C=? where id=?

What would be the bind value of '?' when updating a record with an empty cell? I'm working with iOS if that matters.

Since only some cells are empty, the other option would be to update the table one cell at a time instead of one record at a time. That feels inefficient, however.