When setting a localized Hash field to `nil` after it's been created, the predicate method corresponding to that field does not respect the locale.

Consider the following Mongoid model called "Product":

class Product
  include Mongoid::Document

  field :details, type: Hash, localize: true
end

It has a single, localized attribute called "details". Here's what happens when we try to create a Product using the locale "es":

I18n.locale = :es
product = Product.create details: { foo: 'bar' }
product # => ... details: { "es" => { foo: "bar" } } ...
product.details? # => true
product.details # => { foo: 'bar' }

Now watch what happens after we update the "details" attribute and run the same calls on the model:

product.update details: nil
product # => ... details: { "es" => nil } ...
product.details? # => true
product.details # => nil

This inconsistency would then cause the following example implementation code to fail:

if @product.details?
  @product.details.each { |detail| puts detail }
end

with a very nasty "undefined method each for nil:nilClass" error.