fix grpc server to handle nil

proxy/grpc/server.go

@@ -53,19 +53,28 @@ func (s *proxyInputSrv) SubmitRollupTransaction(ctx context.Context, req *pbseq.
 
 // GetNextBatch returns the next batch of transactions from sequencer to rollup.
 func (s *proxyOutputSrv) GetNextBatch(ctx context.Context, req *pbseq.Batch) (*pbseq.Batch, error) {
-	lastBatch := &sequencing.Batch{}
-	lastBatch.FromProto(req)
+	var lastBatch *sequencing.Batch
+	if req != nil {
+		lastBatch = &sequencing.Batch{}
+		lastBatch.FromProto(req)
+	}
 	batch, err := s.SequencerOutput.GetNextBatch(ctx, lastBatch)
 	if err != nil {
 		return nil, err
 	}
+	if batch == nil {
+		return nil, nil
+	}
 	return batch.ToProto(), nil
 }
 
 // VerifyBatch verifies a batch of transactions received from the sequencer.
 func (s *proxyVerificationSrv) VerifyBatch(ctx context.Context, req *pbseq.Batch) (*pbseq.VerificationResponse, error) {
-	batch := &sequencing.Batch{}
-	batch.FromProto(req)
+	var batch *sequencing.Batch
+	if req != nil {
+		batch = &sequencing.Batch{}
+		batch.FromProto(req)
+	}
 	ok, err := s.BatchVerifier.VerifyBatch(ctx, batch)
 	if err != nil {
 		return nil, err