How cast empty string to null?

[cawa-93]

I have optional text field. I need create validator for type null or undefined or not empty string.

I wrote:

const validator = string().trim().min(1).nullish()

In general, it works. But I would like the empty string to be interpreted as no value and reduced to null or undefined

[StefanTerdell]

z.string().transform(x => x || null)