func (e overlayError) ErrorMsg() string {
	return e.errorMsg
}
ErrorMsg returns the string representation of the overlay error message
package mutate
import "fmt"
type codeKey int
const (
	conditionFailure codeKey = iota
	conditionNotPresent
	overlayFailure
)
type overlayError struct {
	statusCode codeKey
	errorMsg   string
}
func newOverlayError(code codeKey, msg string) overlayError {
	return overlayError{statusCode: code, errorMsg: msg}
}
func (e overlayError) StatusCode() codeKey {
	return e.statusCode
}