proposal: reflect: reflect.TypeOf(nil).Kind() panics; let's make it return nil

[leozz37]

The Kind() method of reflect.TypeOf() returns the type of a given value, so this snippet panics:

import "reflect"

func main() {
    reflect.TypeOf(nil).Kind()
}

panic: runtime error: invalid memory address or nil pointer dereference

When checking the type of a value, may occur that it can be nil, causing the program to crash. Iterating through a slice of interface and having a nil value can be a struggle.

There's many ways to solve this, but my propose is that reflect.TypeOf(nil).Kind() should returns nil.

I'm not sure this makes sense, but brought the topic to discuss.

[robpike]

Duplicate of #51649?

[ianlancetaylor]

Yes, let's fold this into #51649. Thanks.