I was playing around with search_api and zend_lucene as an indexing service . Module installs fine, does find Zend lib in sites/all/libraries and I can create a server in the search_api admin, and can create an index. The files in public://lucene_database are written, but when I run cron to index, I get an error

Invalid argument supplied for foreach() in ZendLuceneService->indexItems() (line 84 of /homes/
/sites/all/modules/zend_lucene/service.inc).

search_api status says the nodes were indexed, but the index is obviously empty (just 3k .cfs file, and search return no results).

Maybe something trivial, but so far my PHP knowledge is limited.