Auto declared error in function has null access panic after checking if it is nil

magic_error.go

package main

import (
	"errors"
	"fmt"
)

type MyError struct {
	error
}

func main() {
	err := funcWithErrors()
	fmt.Println(err)
}

func funcWithErrors() (err error) {
	err = test(-1)
	fmt.Println("-1 error: ", err)
	if err != nil {
		fmt.Println("-1 wow! ", err.Error())
	}
	err = test(0)
	fmt.Println("0 error: ", err)
	if err != nil {  //  err is nil but the condition is true
		fmt.Println("0 wow! ", err.Error()) // so we have a panic here coz null accessing
	}
	err = test(1)
	fmt.Println("1 error: ", err)
	if err != nil {
		fmt.Println("1 wow! ", err.Error())
	}
	return nil
}

func test(a int) *MyError {
	if a >= 0 {
		return nil
	} else {
		return &MyError{errors.New("negative")}
	}
}