def load_defaults_file(file, hash)
      begin
        config = YAML::load_file(file)
      rescue
        raise MigrationError.new("Could not read defaults file #{file}: " + $!)
      end
      # collect the class => path => value entries
      config.each do |path_s, value|
        next if value.nil_or_empty?
        klass, path = create_attribute_path(path_s)
        hash[klass][path] = value
      end
    end
def load_defaults_file(file, hash)
      begin
        config = YAML::load_file(file)
      rescue
        raise MigrationError.new("Could not read defaults file #{file}: " + $!)
      end
      # collect the class => path => value entries
      config.each do |path_s, value|
        next if value.nil_or_empty?
        klass, path = create_attribute_path(path_s)
        hash[klass][path] = value
      end
    end
Loads the defaults config file into the given hash.

 @param [String] file the file to load
 @param [<Class => <String => Object>>] hash the class => path => default value entries