rails/rails — pull request #7970 by scottwillson (2012-10-16 20:13:52+00:00)
Title: Fix duplicate validates_presence_of errors

A recent commit to edge Rails https://github.com/rails/rails/commit/1fab518c6a75dac5773654646eb724a59741bc13
correctly considers marked for destruction associations as blank, but
incorrectly adds a duplicate error for blank has_one and belongs_to associations.

This pull request fixes this.

Example:
Boy.validates_presence_of(:face)
b = Boy.new
b.errors.full_messages

["Face can't be blank", "Face can't be blank"]