def add(error, group_name = :base)
      if error.is_a?(String)
        @error_messages[group_name.to_sym] << error
      elsif error.is_a?(Array)
        @error_messages[group_name.to_sym] += error
      end
    end
def add(error, group_name = :base)
      if error.is_a?(String)
        @error_messages[group_name.to_sym] << error
      elsif error.is_a?(Array)
        @error_messages[group_name.to_sym] += error
      end
    end
available args:
   base_name - name of the default section
   error_messages - Array or String with error message(s) for base section