Mongoid 3.1.4 undefined method 'has_key?' when calling 'Document.create'

I'm having a problem trying to use Mongoid (v 3.1.4) to persist a (really simple) entity to MongoDB (v 2.4.4). I'm using MRI and Ruby 2.0.0-p195 on OS X.

Here's my class (Person.rb):

require 'mongoid'

class Person
  include Mongoid::Document
  include Mongoid::Timestamps # currently can be ommitted

  field :name, type: String

  def initialize
    # is empty
  end

  def name
    @name
  end

  def name=(value)
    @name = value
  end

end

Mongoid.load!('config/mongoid.yml', :development)

user = Person.new
user.name = "John Doe"
user.create

That last sentence greets me with a

[...]mongoid/attributes.rb:320:in 'method_missing': undefined method `has_key?' for nil:NilClass (NoMethodError)

Here's my 'mongoid.yml':

development:
  sessions:
    default:
      database: rbtest
      hosts:
        - localhost:27017
test:
  sessions:
    default:
      database: test
      hosts:
        - localhost:27017
      options:
        consistency: :strong
        max_retries: 1
        retry_interval: 0

Connection to the DB instance seems ok as the DB is created ('rbtest') however, Collections and Documents fail. I've already tried with 'create!' and 'safely.save!' to no avail.

I tried implementing the has_key? method, for which I couldn't find any documentation, so I'm at a bit of a loss here.

As always, any help is much appreciated.

Regards,

---

UPDATE -- SOLUTION:

@Frederik Cheung's answer was spot on. Here's the working code (updated with @mu-is-too-short's suggestion)

require 'mongoid'

class Person
  include Mongoid::Document
  field :name, type: String
end

Mongoid.load!('config/mongoid.yml', :development)

person = Person.new(:name => 'John Doe')
person.save!

The problem is your initialize method: you are overriding the one provided by mongoid, so some of mongoid's internals aren't being setup.

You need to either remove your initialize method or call the mongoid's implementation via super