rails/rails — pull request #6143 by senny (2012-05-03 15:13:35+00:00)
Title: allow the :converter Proc form composed_of to return nil

This makes it possible to filter invalid input values before they are passed
into the value-object (like empty strings). This behaviour is only relevant
if the :allow_nil options is set to true. Otherwise you will get
the resulting NoMethodError.

This pull-request is the same as #3421 but with the correct merge target.