def handle_answer(answer)
      return nil  if answer.nil?
      answer = convert(answer)
      field = opts[:field]
      if field
        answer = answer[field]
      end
      answer
    end
def handle_answer(answer)
      return nil  if answer.nil?
      answer = convert(answer)
      field = opts[:field]
      if field
        answer = answer[field]
      end
      answer
    end
Handles API answer. Take in care `:field` option.
 @param answer API answer field.
 @return Converted answer by default.
 @see #convert
 @see #opts