TypeError [ERR_INVALID_ARG_TYPE]: The "file" argument must be of type string. Received null

here was my command:

```shell
markdown-pdf report-paper-3.md -o $(uuidgen)
```

I got this error

```
node:internal/validators:120
throw new ERR_INVALID_ARG_TYPE(name, 'string', value);
^

TypeError [ERR_INVALID_ARG_TYPE]: The "file" argument must be of type string. Received null
at new NodeError (node:internal/errors:372:5)
at validateString (node:internal/validators:120:11)
at normalizeSpawnArguments (node:child_process:505:3)
at spawn (node:child_process:693:13)
at Object.execFile (node:child_process:327:17)
at WriteStream. (/Users/amills/.nvm/versions/node/v16.15.0/lib/node_modules/markdown-pdf/index.js:117:22)
at WriteStream.emit (node:events:539:35)
at finish (node:internal/streams/writable:754:10)
at finishMaybe (node:internal/streams/writable:739:9)
at afterWrite (node:internal/streams/writable:504:3) {
code: 'ERR_INVALID_ARG_TYPE'
}
```

the error makes no sense to me :( :(