ReferenceError: error is not defined when generating es6 js for proto3 file

[hipresario]

protobuf.js version: 6.6.5

I have a proto3 file:
syntax = "proto3"; package test; message Block { string name = 1; repeated Node inputs = 2; repeated Node outputs = 3; } message Node { string id = 1; string name = 2; }
The generated js as follows when compiled using -w es6:

Block.verify = function verify(message) {
                        if (typeof message !== "object" || message === null)
                            return "object expected";
                        if (message.name != null && message.hasOwnProperty("name"))
                            if (!$util.isString(message.name))
                                return "name: string expected";
                        if (message.inputs != null && message.hasOwnProperty("inputs")) {
                            if (!Array.isArray(message.inputs))
                                return "inputs: array expected";
                            for (let i = 0; i < message.inputs.length; ++i) {
                                let error = $root.test.Node.verify(message.inputs[i]);
                                if (error)
                                    return "inputs." + error;
                            }
                        }
                        if (message.outputs != null && message.hasOwnProperty("outputs")) {
                            if (!Array.isArray(message.outputs))
                                return "outputs: array expected";
                            for (let i = 0; i < message.outputs.length; ++i) {
                                error = $root.test.Node.verify(message.outputs[i]);
                                if (error)
                                    return "outputs." + error;
                            }
                        }

ReferenceError: error is not defined
    at Function.verify (compiled.pb.js:75363)

I think there is a bug when declaring the error using let, i.e. scope issue. the _ let error = $root.test.Node.verify(message.inputs[i]);_ not visible in the below code block.