You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: marshal_proto.go
    path of file: ./repos/moby/vendor/github.com/grpc-ecosystem/grpc-gateway/v2/runtime
    
    the code of the file until where you have to start completion: package runtime

import (
	"errors"
	"io"

	"google.golang.org/protobuf/proto"
)

// ProtoMarshaller is a Marsha
    
func (*ProtoMarshaller) Unmarshal(data []byte, value interface{}) error {
	message, ok := value.(proto.Message)
	if !ok {
		return errors.New("unable to unmarshal non proto field")
	}
	return proto.Unmarshal(data, message)
}