Fix bug where exception is thrown when csv source key does not exist …

[graytaylor0]

…or is null

Description

If the source specified in the csv processor does not exist in the Event or contains a null value in the Event, an exception is thrown and the Events are dropped

ava.lang.IllegalArgumentException: argument "content" is null
    at com.fasterxml.jackson.databind.ObjectReader._assertNotNull(ObjectReader.java:2456) ~[jackson-databind-2.15.2.jar:2.15.2]
    at com.fasterxml.jackson.databind.ObjectReader.createParser(ObjectReader.java:1154) ~[jackson-databind-2.15.2.jar:2.15.2]
    at com.fasterxml.jackson.databind.ObjectReader.readValues(ObjectReader.java:1943) ~[jackson-databind-2.15.2.jar:2.15.2]
    at org.opensearch.dataprepper.plugins.processor.csv.CsvProcessor.doExecute(CsvProcessor.java:66) ~[csv-processor-2.4.0-SNAPSHOT.jar:?]
    at org.ope

This fixes that bug so that it is a no-op and the Event continues processing through the pipeline

Issues Resolved

Check List

• New functionality includes testing.
• New functionality has been documented.
  • New functionality has javadoc added
• Commits are signed with a real name per the DCO

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