You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: allow_mass_assignment.rb
    path of file: ./repos/mongoid-rspec/lib/matchers
    
    the code of the file until where you have to start completion: # this code is totally extracted from shoulda-matchers gem.
module Mongoid
  module Matchers
    class AllowMassAssignmentOfMatcher # :nodoc:
      attr_reader :failure_message, :negative_failure_message
      alias failure_message_when_negate
    
      def matches?(klass)
        @klass = klass
        if attr_mass_assignable?
          if whitelisting?
            @negative_failure_message = "#{@attribute} was made accessible"
          else
            if protected_attributes.empty?
              @negative_failure_message = 'no attributes were protected'
            else
              @negative_failure_message = "#{class_name} is protecting " \
                                          "#{protected_attributes.to_a.to_sentence}, " \
                                          "but not #{@attribute}."
            end