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

[graytaylor0]

… events

Description

This change fixes a bug where

Recreating

1. Create a pipeline with two processors, where the first drops all events

processor:
   - drop_events:
         drop_when: true
   - add_entries:
         ....

2. Observe the error and shut down of the process worker

ERROR org.opensearch.dataprepper.pipeline.ProcessWorker - Encountered exception during pipeline log-pipeline processing
java.lang.ClassCastException: class java.util.Collections$EmptyList cannot be cast to class java.util.ArrayList (java.util.Collections$EmptyList and java.util.ArrayList are in module java.base of loader 'bootstrap')
	at org.opensearch.dataprepper.pipeline.ProcessWorker.doRun(ProcessWorker.java:132) ~[data-prepper-core-2.7.0-SNAPSHOT.jar:?]
	at org.opensearch.dataprepper.pipeline.ProcessWorker.run(ProcessWorker.java:62) [data-prepper-core-2.7.0-SNAPSHOT.jar:?]
	at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515) [?:?]
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264) [?:?]
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) [?:?]
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) [?:?]
	at java.base/java.lang.Thread.run(Thread.java:829) [?:?]

Issues Resolved

Resolves #[Issue number to be closed when this PR is merged]

Check List

• New functionality includes testing.
• New functionality has a documentation issue. Please link to it in this PR.
  • New functionality has javadoc added
• Commits are signed with a real name per the DCO

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[dlvenable]

@graytaylor0 , It would be ideal to have a unit test which tests against an empty list since that is the exact cause of the bug.