As Irina mentioned on SERVER-68743:

Also, the refactor from SERVER-68713 preserved the defensive wrappers, such as makeFillEmptyFalse, which are not needed when generating per-path filters in CSI. It would be nice to avoid injecting them.

There is also a question of whether we want to do this by simply passing a flag to the code which generates the expressions, or if we want to optimize the expressions/bytecode given the constraint that the slot holding the column's value is not Nothing.