private void invokeRpcIfValidConnection(Request request) {
            if (target.isValid()) {
                target.invokeSync(request, Duration.ofMinutes(10));
            } else {
                throw new RuntimeException("Connection to " + target + " is invalid", target.getConnectionLostReason());
            }
        }
Returns true if empty sentinel config can be returned when a request from a host that is
not part of an application asks for sentinel config
configserver/src/main/java/com/yahoo/vespa/config/server/rpc/RpcServer.java