I did a git bisect: with commit 73da84a definition look up works, with commit 0325b78 it breaks and only an empty buffer is shown.
Status line is in both cases identical:
[LC] jdt://contents/jena-core-3.10.0.jar/org.apache.jena.graph/Triple.class?=nifi-sparql-integrate-processors/%5C/home%5C/XXXX%5C/.m2%5C/repository%5C/org%5C/apache%5C/jena%5C/jena-core%5C/3.10.0%5C/jena-core-3. 10.0.jar%3Corg.apache.jena.graph(Triple.class 37:14