# File lib/pdf/reader/object_hash.rb, line 168
    def has_key?(check_key)
      # TODO update from O(n) to O(1)
      each_key do |key|
        if check_key.kind_of?(PDF::Reader::Reference)
          return true if check_key == key
        else
          return true if check_key.to_i == key.id
        end
      end
      return false
    end