rails/rails — pull request #12746 by coreyward (2013-11-02 22:30:57+00:00)
Title: Fix Hash#deep_merge bug and improve documentation — resolves #12738

Previously merging into a hash with a falsy value would not result in
the merge-block being called. The fix is simply to check for presence
of the key in the hash.

The documentation example for `deep_merge` now appropriately
demonstrates what a deep merge does.