CREATE TABLE table_3012 ("District" TEXT, "Vacator" TEXT, "Reason for change" TEXT, "Successor" TEXT, "Date successor seated" TEXT)

Who was the vacator for the district of Nebraska at-large?
SELECT "Vacator" FROM table_3012 WHERE "District" = 'Nebraska At-large'
SELECT "Vacator" FROM "table_3012" WHERE "District" = 'Nebraska At-large'