http://edgeguides.rubyonrails.org/4_2_release_notes.html#active-record-d
eprecations
> Deprecated passing Active Record objects to .find or .exists?. Call
id on the objects first.
Commits in Rails:
https://github.com/rails/rails/commit/d92ae6ccca3bcfd73546d612efaea01127
0bd270
https://github.com/rails/rails/commit/d35f0033c7dec2b8d8b52058fb8db495d4
9596f7
https://github.com/rails/rails/commit/c0609dd0f0f0de604ac1ffeffdf5e3e0e7
356b35