Using allow after valid is not working

[Pnlvfx]

Describe the bug
If you add the allow operator after using the valid it will only pick the valid.

example:

export const ciaoSchema = Joi.string().valid('Ciao').allow(null).meta({className: 'Data'})

will output:

type Data = 'Ciao'

instead of:

type Data = 'Ciao' | null

[Pnlvfx]

Describe the bug If you add the allow operator after using the valid it will only pick the valid.

example:

export const ciaoSchema = Joi.string().valid('Ciao').allow(null).meta({className: 'Data'})

will output:

type Data = 'Ciao'

instead of:

type Data = 'Ciao' | null

I know That I can add the null on the valid, but when you have a reusable type it's not always possible to do so.