Thx for reporting the Bug, to fix it you have to add the following code to your SolrConnectorStore.php line 39
/**
* Return status of the concept cache for the given concept as an array
* with key 'status' ('empty': not cached, 'full': cached, 'no': not
* cachable). If status is not 'no', the array also contains keys 'size'
* (query size), 'depth' (query depth), 'features' (query features). If
* status is 'full', the array also contains keys 'date' (timestamp of
* cache), 'count' (number of results in cache).
*
* @param $concept Title or SMWWikiPageValue
*/
public function getConceptCacheStatus( $concept ) {
return self::getBaseStore()->getConceptCacheStatus( $concept );
}