When you delete item number 4 from a list, the old number 5 is moved down to become the new number 4. That's the definition of deleting an entry from the list.
If you'd like the list to contain a null (or an empty
String, or whatever) at that position instead, then don't delete the item; just set that element to the contents you want -- i.e.,
theList.set(4, null);