Following the rework of the `:class_name` option in v7.0.3, a value of '::SomeClass' causes a NameError exception. GitHub PR #4640 fixes it so it works again (as it did in 7.0.2 and prior).

Example:
class Child
  include Mongoid::Document
  belongs_to :parent, class_name: '::OtherClass'
{{ end}}