CREATE TABLE table_204_507 (id DECIMAL, "bridge name" TEXT, "location" TEXT, "year completed" DECIMAL, "total length" TEXT, "carries" TEXT)

what was the shortest bridge mccullough designed ?
SELECT "bridge name" FROM table_204_507 ORDER BY "total length" LIMIT 1
SELECT "bridge name" FROM "table_204_507" ORDER BY "total length" NULLS FIRST LIMIT 1