staticman: Error thrown from NodeRSA.js:178 "Empty key given" when attempting to start the server

I followed your steps on https://github.com/eduardoboucas/staticman:

1. Clone the repository and install the dependencies via npm
2. Create a development config file from the sample file.
3. Edit the newly-created config file with your GitHub access token, SSH private key and the port to run the server.
4. I additionally run export NODE_ENV=development
5. Start the server.

When I start the server I get the following error:

martm106-3AH03Y:staticman martm106$ npm start

> staticman@2.0.0 prestart /Users/martm106/Dev/staticman
> if [ ! -d node_modules ]; then npm install; fi


> staticman@2.0.0 start /Users/martm106/Dev/staticman
> node index.js

/Users/martm106/Dev/staticman/node_modules/node-rsa/src/NodeRSA.js:178
            throw Error("Empty key given");
            ^

Error: Empty key given
    at NodeRSA.module.exports.NodeRSA.importKey (/Users/martm106/Dev/staticman/node_modules/node-rsa/src/NodeRSA.js:178:19)
    at Object.<anonymous> (/Users/martm106/Dev/staticman/controllers/encrypt.js:8:5)
    at Module._compile (module.js:569:30)
    at Object.Module._extensions..js (module.js:580:10)
    at Module.load (module.js:503:32)
    at tryModuleLoad (module.js:466:12)
    at Function.Module._load (module.js:458:3)
    at Module.require (module.js:513:17)
    at require (internal/module.js:11:18)
    at new StaticmanAPI (/Users/martm106/Dev/staticman/server.js:13:14)
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! staticman@2.0.0 start: `node index.js`
npm ERR! Exit status 1
npm ERR! 
npm ERR! Failed at the staticman@2.0.0 start script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /Users/martm106/.npm/_logs/2017-07-26T13_49_18_210Z-debug.log

Any hint how to resolve?

Node v8.2.1 MacOS Sierra v10.12.5