When using full text search, in GUI or API, empty items are appearing in the response.
See examples below:

Search for "visualization", empty item with score 5 after "Paintera", and item with score 4 two lines further down.
http://biii.eu/search?search_api_fulltext=visualization

Same search with JSON export, empty item highlighted:
http://biii.eu/searchjsonexport?search_api_fulltext=(?=visualization)&_format=json