Error: Arguments to path.resolve must be strings

I found this error on console and I noticed that it is caused by this package and by the [atom-color-highlight](https://github.com/abe33/atom-color-highlight/) package.

It occurs when I launch Atom and I have one of your packages enabled. It occurs even when I try to enable one of the two package.

I'm using Atom Version `0.177.0`.

```
Arguments to path.resolve must be strings TypeError: Arguments to path.resolve must be strings
at Object.posix.resolve (path.js:423:13)
at new PathScanner (/Applications/Atom.app/Contents/Resources/app/node_modules/scandal/lib/path-scanner.js:25:28)
at Object.module.exports (/Applications/Atom.app/Contents/Resources/app/src/scan-handler.js:12:15)
at process. (/Applications/Atom.app/Contents/Resources/app/src/task-bootstrap.js:84:10)
at process.emit (events.js:119:17)
at handleMessage (child_process.js:326:10)
at Pipe.channel.onread (child_process.js:354:11)
```

The error originates in path-scanner.js line 25, where path.resolve receives a non-string argument. Examine the PathScanner constructor in the scandal package to see what input is being passed. Check how the package scans for project colors and what might cause a non-string path. Look at the scan-handler.js and task-bootstrap.js in Atom's source to understand the invocation context.

Written by the indexing model from the issue text.