Hi,
We have recently introduced the breaking change in vdsm-jsonrpc-java [1]. Reactive streams package has been replaced with java.util.concurrent.Flow (shipped with JDK). This change is released with vdsm-jsonrpc-java-1.6.0.
This change had to be reflected in ovirt-engine as well (otherwise it would not compile). I was handled by this patch [2].
Unfortunately these two changes must be in sync. Please update vdsm-jsonrpc-java to 1.6.0 if you are already working on ovirt engine revision that includes  [2].

[1] https://gerrit.ovirt.org/#/c/vdsm-jsonrpc-java/+/109916/
[2] https://gerrit.ovirt.org/#/c/ovirt-engine/+/112347/

Please accept my apologies for not letting you know earlier, ideally before these patches got merged.

--
Artur Socha
Senior Software Engineer, RHV
Red Hat