How to handle directives without arguments?

```
input EditWidth {
  width: BigDecimal @Positive @Digits(integer: 10, fraction: 2)
}
```

How to handle the `Positive` directive?

this format always expects arguments
```
directive:
   arg1: schemaApi
   arg2: ["schemaApi2", "Hello $1"]
```

It would be ideal to be able to define directive mapping without arguments like:
```
directives: {
  Positive: "positive"
}
```