Adds a null check when reading an S3EventNotification for records. So…

[dlvenable]

Description

Some recent change has SqsWorkerTest failing. resulted in ObjectMapper::treeToValue return null for an empty string.

SqsWorkerTest > processSqsMessages_should_not_interact_with_S3Service_if_input_is_not_valid_JSON(String) > [1]  FAILED
    java.lang.NullPointerException: Cannot invoke "org.opensearch.dataprepper.plugins.source.s3.S3EventNotification.getRecords()" because "s3EventNotification" is null

SqsWorkerTest > WithSuccessfulDeletion > processSqsMessages_should_invoke_delete_if_input_is_not_valid_JSON_and_delete_on_error(String) > [1]  FAILED
    java.lang.NullPointerException: Cannot invoke "org.opensearch.dataprepper.plugins.source.s3.S3EventNotification.getRecords()" because "s3EventNotification" is null

Upon debugging I see that objectMapper.treeToValue(eventNode, S3EventNotification.class); is being called with an empty string and returning null.

The solution is to add a null check.

Issues Resolved

N/A

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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