private int sendMeta(FileReferenceData fileData) {
            Request request = createMetaRequest(fileData);
            invokeRpcIfValidConnection(request);
            if (request.isError()) {
                log.log(WARNING, () -> "Failed delivering meta for reference '" + fileData.fileReference().value() +
                        "' with file '" + fileData.filename() + "' to " +
                        target.toString() + " with error: '" + request.errorMessage() + "'.");
                return 1;
            } else {
                if (request.returnValues().get(0).asInt32() != 0) {
                    throw new IllegalArgumentException("Unknown error from target '" + target.toString() + "' during rpc call " + request.methodName());
                }
                return request.returnValues().get(1).asInt32();
            }
        }
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