added fix for the case that sbi in the received sbi from GetDevice is nil

northbound/server/pnd.go

@@ -121,14 +121,18 @@ func fillOnds(pnd networkdomain.NetworkDomain, all bool, did ...string) ([]*ppb.
 			log.Error(err)
 			return nil, status.Errorf(codes.Aborted, "%v", err)
 		}
+
+		sbi := spb.SouthboundInterface{}
+		if d.SBI() != nil {
+			sbi.Id = d.SBI().ID().String()
+			sbi.Type = d.SBI().Type()
+		}
+
 		onds[i] = &ppb.OrchestratedNetworkingDevice{
 			Id:     id,
 			Name:   d.Name(),
 			Device: dev,
-			Sbi: &spb.SouthboundInterface{
-				Id:   d.SBI().ID().String(),
-				Type: d.SBI().Type(),
-			},
+			Sbi:    &sbi,
 		}
 	}