func IsNotFound(err error) bool {
	err = Cause(err)
	_, ok := err.(*notFound)
	return ok
}
IsNotFound reports whether err was created with NotFoundf() or
NewNotFound().
package errors
import (
	"fmt"
)
func wrap(err error, format, suffix string, args ...interface{}) Err {
	newErr := Err{
		message:  fmt.Sprintf(format+suffix, args...),
		previous: err,
	}
	newErr.SetLocation(2)
	return newErr
}
type notFound struct {
	Err
}
func NotFoundf(format string, args ...interface{}) error {
	return &notFound{wrap(nil, format, " not found", args...)}
}
func NewNotFound(err error, msg string) error {
	return &notFound{wrap(err, msg, "")}
}