public <T extends ContentHandlerWithResult<?>> Builder registerContentHandler(
        Class<T> handlerClass) {
      Type type =
          resolveLastTypeParameter(
              checkNotNull(handlerClass, "handlerClass"), ContentHandlerWithResult.class);
      return registerContentHandler(
          type, new NewInstanceContentHandlerWithResultFactory(handlerClass));
    }
Will call {@link Constructor#newInstance(Object...)} on {@code handlerClass} for each content
stream.

<p>

<h3>Note</h3>

<br>
While this is costly vs {@code new}, it may not affect real performance due to the high cost
of reading streams.

@throws IllegalArgumentException if there's no no-arg constructor on {@code handlerClass}.
sax/src/main/java/feign/sax/SAXDecoder.java