What causes "error marshaling: proto: Marshal called with nil" in hyperledger/fabric?

Use an official, unmodified configtxlator binary matching your Fabric version.

error marshaling: proto: Marshal called with nil

Error message

error marshaling: proto: Marshal called with nil

What it means

In `encodeProto` (cmd/configtxlator/main.go:147), after successful JSON decoding, `msg` was still nil, so calling `proto.Marshal` would fail with 'proto: Marshal called with nil'. This is a defensive guard inside configtxlator; in practice it is nearly unreachable because DeepUnmarshalJSON would already have failed on a nil message.

Source

Thrown at cmd/configtxlator/main.go:147

	mt, err := protoregistry.GlobalTypes.FindMessageByName(protoreflect.FullName(msgName))
	if err != nil {
		return errors.Wrapf(err, "error encode input")
	}

	msgType := reflect.TypeOf(mt.Zero().Interface())

	if msgType == nil {
		return errors.Errorf("message of type %s unknown", msgType)
	}
	msg := reflect.New(msgType.Elem()).Interface().(proto.Message)

	err = protolator.DeepUnmarshalJSON(input, msg)
	if err != nil {
		return errors.Wrapf(err, "error decoding input")
	}

	if msg == nil {
		return errors.New("error marshaling: proto: Marshal called with nil")
	}
	out, err := proto.Marshal(msg)
	if err != nil {
		return errors.Wrapf(err, "error marshaling")
	}

	_, err = output.Write(out)
	if err != nil {
		return errors.Wrapf(err, "error writing output")
	}

	return nil
}

func decodeProto(msgName string, input, output *os.File) error {
	mt, err := protoregistry.GlobalTypes.FindMessageByName(protoreflect.FullName(msgName))
	if err != nil {
		return errors.Wrapf(err, "error encode input")

View on GitHub (pinned to 2736b63f8f)

Solutions

Use an official, unmodified configtxlator binary matching your Fabric version.
Verify the input decodes correctly by first running `configtxlator proto_decode` on a known-good .pb to produce valid JSON.
If building from source, ensure reflect.New(msgType.Elem()) produces a non-nil proto.Message.

Defensive patterns

Strategy: try-catch

Try / catch

out, err := exec.Command("configtxlator", "proto_encode", ...).CombinedOutput()
if err != nil && strings.Contains(string(out), "Marshal called with nil") {
	log.Printf("configtxlator binary defect suspected; rebuild from official release: %s", out)
}

Prevention

Use official configtxlator binaries; this guard is effectively unreachable in standard builds.
Rebuild cleanly from matching Fabric source tags if you maintain a custom binary.
Treat occurrences as a tooling bug, not an input problem.

When it happens

Trigger: Theoretically triggered when the decoded message ends up nil after DeepUnmarshalJSON succeeds — e.g. a degenerate/custom build where the reflect-constructed message is nil. Standard usage of `configtxlator proto_encode` does not hit this.

Common situations: Custom or patched configtxlator builds; pathological input where a nil message is constructed; version drift in protolator/proto helpers.

Related errors

AI-assisted analysis of hyperledger/fabric@2736b63f8f (2026-09-04). Data as JSON: /api/errors/01e900fdba955495. Report an issue: GitHub.