What was the date of the game with a decision of Niittymaki and when the Flyers had a record of 30–21–5?
CREATE TABLE "regular_season" (
  "date" text,
  "visitor" text,
  "score" text,
  "home" text,
  "decision" text,
  "attendance" real,
  "record" text
);
SELECT "date" FROM "regular_season" WHERE "decision"='niittymaki' AND "record"='30–21–5';