nil has type, it can be a receiver.

main.go

package main

import "fmt"

type A struct {
	a string
}

func NewA(strp *string) *A {
	if strp == nil {
		return nil
	}
	return &A{a: *strp}
}

func (a *A) GetA() *string {
	if a == nil {
		return nil
	}
	return &a.a
}

func main() {
	str := "hello"
	a1 := NewA(&str)
	fmt.Printf("a1: %#v, a1.GetA() = %#v\n", a1, a1.GetA()) // a1: &main.A{a:"hello"}, a1.GetA() = (*string)(0xc000010250)
	a2 := NewA(nil)
	fmt.Printf("a2: %#v, a2.GetA() = %#v\n", a2, a2.GetA()) // a2: (*main.A)(nil), a2.GetA() = (*string)(nil)
}