@Override
        public void onError(Throwable t) {
            if (this.error == null) {
                this.error = t;
            } else {
                this.error.addSuppressed(t);
            }
            this.completed = true;
        }
Helper class used to check that the scoped responses are different per request, but the same for different
messages in the same request.
tests/src/test/java/net/devh/boot/grpc/test/scope/GrpcRequestScopeTest.java