Fix bug where process worker would shut down if a processor drops all…

… events

Signed-off-by: Taylor Gray <tylgry@amazon.com>

data-prepper-core/src/main/java/org/opensearch/dataprepper/pipeline/ProcessWorker.java

@@ -129,7 +129,7 @@ private void doRun() {
 
             List<Event> inputEvents = null;
             if (acknowledgementsEnabled) {
-                inputEvents = ((ArrayList<Record<Event>>) records).stream().map(Record::getData).collect(Collectors.toList());
+                inputEvents = ((List<Record<Event>>) records).stream().map(Record::getData).collect(Collectors.toList());
             }
 
             try {