The word '(empty)' is seen in reference fields without a value set on lists where the cell was previously blank.
This behavior change is made in the following versions: KP10, LP2, M
This was an intentional change made to resolve a problem PRB1004508, which was a longstanding bug that was preventing the text from rendering previously. The addition of "(empty)" was to help make it clear that the cell is actually empty/valueless rather than just an empty string value. This is helpful in general but it's especially valuable for accessibility purposes since screenreader users used to get silence about the cell's value instead of being told explicitly that it is empty.