SELECT DISTINCT name FROM Reviewer AS T1 JOIN Rating AS T2 ON T1.rID  =  T2.rID WHERE ratingDate  =  "null"
What are the different names of all reviewers whose ratings do not have a date field?
[Schema (values) (types)]: | movie_1 |  Movie : mid (text) , title (number) , year (text) , director (number) | Reviewer : rid (text) , name (number) | Rating : rid (text) , mid (number) , stars (text) , ratingdate (number);