data in openapi-fetch is a string, not object

[kitadakyou]

I ran the following code, I noticed that the type of data is string.
This behavior is normal for the fetch function.
However, in TypeScript, it is inferred as object, and when I run JSON.parse(data), I get a type error.
Why is this happening?

const { data }  = await client.GET("/test")
console.log(typeof data) // string

console.log(data.userId) // undefined

const json = JSON.parse(data) // It works but type error
console.log(json.userId) // returns expected value