I don't understand why useSWR can accept null as its first argument.

[TakahiroHimi]

Hello!

What I don't understand is the following part of the source.

https://github.com/vercel/swr/blob/master/src/types.ts#L6-L32

The first argument of useSWR determines the type of Fetcher.
If the first argument is null, it appears to enter the never branch in the fourth line from the bottom and cause an error, but in fact, even if null is entered, it enters the other branches and is valid.
Why does it behave this way without entering the never branch?

Thanks in advance!

[TakahiroHimi]

I solved the problem.

It was caused by strict:false in tsconfig.json.