fails with es6 class member functions

[psnider]

version 0.4.0
node v6.9.1

When I enter this code in the node REPL:

var promisify = require("promisify-node");
class C {
    constructor() {
        this.promisified_connect = promisify(this.connect);
    }
    connect(done) {
        if (done) {
            done();
        } else {
            return this.promisified_connect();
        }
    }
}
var c = new C()

promisify-node throws this error:

TypeError: Cannot read property '1' of null
    at module.exports (./node_modules/promisify-node/utils/args.js:9:63)
    at processExports (./node_modules/promisify-node/index.js:61:29)
    at module.exports (./node_modules/promisify-node/index.js:164:10)

so I updated the RegExp in https://github.com/nodegit/promisify-node/blob/master/utils/args.js#L9 from:

/function\s.*?\(([^)]*)\)/

to:

/\(([^)]*)\)/

Then re-running the above test code produced another error:

TypeError: Cannot convert undefined or null to object
    at processExports (./node_modules/promisify-node/index.js:86:16)
    at module.exports (./node_modules/promisify-node/index.js:164:10)
    at new C (repl:3:28)

I was able to get past this by modifying https://github.com/nodegit/promisify-node/blob/master/index.js#L86 to guard the checking of the keys of the prototype to:

    if (exports.prototype) {
      if (Object.keys(exports.prototype).length) {

I believe there are likely other changes required.