Steps to reproduce:

1. Content type with email field type
2. Create content of this type
3. Fill in email address (eg "abc@def.com")
4. Publish content
5. Edit content
6. Change at least one character of mail address from lovwercase to uppercase (or the other way around) (eg "abc@Def.com")
7. Publish

This leads to the following error:

php.CRITICAL: Uncaught Error: Argument 5 passed to eZ\Publish\Core\Search\Legacy\Content\WordIndexer\Repository\SearchIndex::addObjectWordLink() must be of the type int, null given, called in .../vendor/ezsystems/ezplatform-kernel/eZ/Publish/Core/Search/Legacy/Content/WordIndexer/Gateway/DoctrineDatabase.php on line 266 {"exception":"[object] (TypeError(code: 0): Argument 5 passed to eZ\\Publish\\Core\\Search\\Legacy\\Content\\WordIndexer\\Repository
SearchIndex::addObjectWordLink() must be of the type int, null given, called in .../vendor/ezsystems/ezplatform-kernel/eZ/Publish/Core/Search/Legacy/Content/WordIndexer/Gateway/DoctrineDatabase.php on line 266 at .../vendor/ezsystems/ezplatform-kernel/eZ/Publish/Core/Search/Legacy/Content/WordIndexer/Repository/SearchIndex.php:120)"}