@Override
            String getDocumentJson(long start, long end) {
                String payload = new String(copy(start, end), UTF_8);
                synchronized (lock) {
                    tail = end;
                    lock.notify();
                }
                return payload;
            }
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