rails/rails — pull request #12547 by derekprior (2013-10-15 17:14:04+00:00)
Title: Pluck on NullRelation should accept a list of columns

In Rails 4, `pluck` was updated to accept a list of columns, but the `NullRelation`
was never updated to match that signature. As a result, calling `pluck`
with multiple columns on a `NullRelation` results in an `ArgumentError`.