rails/rails — pull request #9117 by manlycode (2013-01-29 22:55:09+00:00)
Title: Fix #8832 - Fixes a regression introduced in 3.0.19

in ActionPack due to empty hashes and arrays in
params being replaced with nil.

Because actionpack now strips empty collections from
params, this causes NestedAttributes::assign_nested_attributes_for_collection_association to raise an ArgumentError.

This commit fixes that behavior by defaulting nil
collections to an empty hash.