def check_validity!
      raise ArgumentError, "Options must include :from" unless options.include?(:from)
      raise ArgumentError, "Options must include :to" unless options.include?(:to)
      raise ArgumentError, "Options cannot specify array for :to" if options[:to].is_a?(Array)
    end
def check_validity!
      raise ArgumentError, "Options must include :from" unless options.include?(:from)
      raise ArgumentError, "Options must include :to" unless options.include?(:to)
      raise ArgumentError, "Options cannot specify array for :to" if options[:to].is_a?(Array)
    end
:nodoc: