There's line in users factory for mail `f.sequence(:mail) { |n| "username#{n}@testing.com" }` but it still causes PG error for null value:

`PG::Error: ERROR:  null value in column "mail" violates not-null constraint
: UPDATE "users" SET "updated_at" = '2013-12-30 19:05:49.401963', "mail" = NULL WHERE "id" = 1293`