Some reviewers didn't provide a date with their rating.

Find the names(name) of all reviewers who have ratings with a NULL value for the date.

You can find the full data description here

movie ( mID, title, year, director )

English: There is a movie with ID number mID, a title, a release year, and a director.

reviewer ( rID, name )

English: The reviewer with ID number rID has a certain name.

rating ( rID, mID, stars, ratingDate )

English: The reviewer rID gave the movie mID a number of stars rating (1-5) on a certain ratingDate.