rails/rails — pull request #13371 by vipulnsward (2013-12-18 09:53:16+00:00)
Title: Assigning nil to a polymorphic belongs_to should nullify its _type column

Assigning nil to a polymorphic belongs_to should nullify its _type column

Fixes failing test introduced at c141dfc838a5dca9f197814410fa5d44c143129c by @jeremy