Better error message for an empty command

Say I have a script like:

`"script": { "lint": "npm run eslint && npm run prettier" }`

in wireit, i might do:

```
"wireit": {
"lint": {
"dependencies": [ "lint", "prettier" ],
"command": "?"
}
}
```

I tried this and get an error when I don't have a command for 'lint'. I am currently using `echo ''` which is fine.
Is there anything wrong with this approach? I wonder if there's a way to do this where the command is empty? If not could / should there be?