Rails 3.2 to 4.0 Upgrade: Undefined method to_datetime for false:FalseClass

I'm upgrading a Rails application I've inherited from 3.2 to 4.0.1. I followed and finished the edge guide here:

http://ift.tt/YwRK6e

I've gotten everything fixed except for a single error that I can't seem to find the root cause of. When I attempt to save a User model object, I'm met with the following error:

[1] pry(main)> User.create(name: "test user", email: "testuser@frobnitz.com", password: "testPassword123", password_confirmation: "testPassword123")                                                                                                                               

(0.6ms)  BEGIN
(0.9ms)  ROLLBACK
NoMethodError: undefined method `to_datetime' for false:FalseClass
from /home/cmhobbs/src/serve2perform/.gem/ruby/2.3.0/gems/activesupport-4.0.1/lib/active_support/core_ext/date_time/calculations.rb:161:in `<=>'

activesupport 4.0.1 and rals 4.0.1 are installed. I use chgems and I purged my .gem/ directory and Gemfile.lock before bundling again.

Here is a Gist of the User model.

And here is all of the backtrace output I could get from pry.