The word "(empty)" is seen in reference fields without a value on lists where the cell was previously blank.
This behavior change is made in versions: KP10, LP2, M
This intentional change was made to resolve a Known Problem (see KB0696733 for more information), which was a longstanding bug that was preventing the text from rendering. 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.