ElasticIndexBulkCronWorker throwing NoMethodError for epics

What does this MR do and why?

This change enhances the efficiency and reliability of a component that loads namespace data by refining the input list. Specifically, it removes any duplicate namespaces and filters out any empty/null entries before processing them. This prevents unnecessary work from being done on duplicate items and avoids potential errors from trying to process invalid data.

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Related to #464366 (closed)