Update mode doesn't allow to set empty a specific field

Use case: A user has a structured document with several fields, and want to update only one of them to delete its content, to set it to blank.
Currently it's no doable with the update choice of the Batch import application, because empty cells on the Excel file are ignored.
Only the use of the "erase" can allow this, but it requires as well to fill all the existing fields to not lose existing data, which is not convenient at all, and may cause errors.

Improvement needed:

• Add the possibility for the user to choose whether he wants to update the empty cells of the Excel file, or not