For use with https://github.com/chancancode/json_expressions. Allows you to write either(FooClass, BarClass). Useful if you're expecting nils.

json_expression_helper.rb

module JsonExpressionHelper
  def either *klasses
    Class.new(Object) do
      @klasses = klasses
      def self.===(other)
        @klasses.reduce(false) { |memo, klass| memo ||= (other.class == klass) }
      end
    end
  end
end