Fixing an issue that type 'null' and 'undefined' is not assignable to validateStatus when typescript strict option is enabled #3200
In previous my PR(#2773), I had missed about two things.
So I fix above things in this PR.
Before -> validateStatus?: ((status: number) => boolean | null)
After - validateStatus?: ((status: number) => boolean) | null
TS2345 Error of line 341, 345 is irrelevant to the validateStatus option. So I don't care about this.