[BUGFIX] Indexer tries to insert NULL into DB

The Indexer of indexed_search tries to insert NULL values
into NOT NULL columns of the database.

Since #53662 NULL values are passed to the database,
hence these insert statements now fail.

Resolves: #54917
Releases: 6.2
Change-Id: Ia935abe14b9c3be2062f1b38ec98fb63921a1c2f
Reviewed-on: https://review.typo3.org/26757
Reviewed-by: Georg Ringer
Tested-by: Georg Ringer