@Override
        String getDocumentJson(long start, long end) {
            return "{\"fields\":" + new String(json, (int) start, (int) (end - start), UTF_8) + "}";
        }
Same as {@link #feedMany(InputStream, ResultCallback)}, but without a provided {@link ResultCallback} instance.
@see JsonFeeder#feedMany(InputStream, ResultCallback) for details.
vespa-feed-client-api/src/main/java/ai/vespa/feed/client/JsonFeeder.java