An error occurred while creating the index: null

[KonradHoeffner]

The folder contains exactly one syntactically correct Turtle file:

/tmp$ du -hs snik/*
3.6M	snik/snik.ttl
/tmp$ rapper -i turtle -c snik/snik.ttl 
rapper: Parsing URI file:///tmp/snik/snik.ttl with parser turtle
rapper: Parsing returned 81494 triples

createIndex throws an error:

/tmp$ docker run aksw/kbox -createIndex snik
Creating index.
An error occurred while creating the index: null