Not sure if FindEntity is intended to support query by "type" property, but in any event, this crashes the server (Running docker container intellabs/vdms:latest)

To reproduce:

Send FindEntity query like:

"FindEntity" : {
         "class" : "Hike", 
         "constraints" : {
             "type" : [] 
         }

While this query has no type value, I think you can reproduce by providing values as well.
Error:

vdms: src/PMGDQuery.cc:339: void VDMS::PMGDQuery::parse_query_constraints(const Json::Value&, VDMS::PMGDQueryConstraints*): Assertion `predicate.size() == 2 || predicate.size() == 4' failed.

Looks like some additional validation is needed, but I haven't dug too deep into it.