JabRef 5.0.0-dev--2019-11-16----3fbeef03d
Mac OS X 10.13.6 x86_64
Java 13.0.1

Steps to reproduce:

1. Select any entry from an open bibliography.
2. Double left click on entry to show the different fields in the lower portion of the window.
3. The right hand side shows "Error while generating citation style", instead of a preview of the citation.

Jabref-5.0.0 has been in this state for a couple of development snapshots.

I have configured APA style, but I get the same "Error while generating citation style" with other styles. I get the same error for all entries in the bibliography.