missing error arg

greetings.go

@@ -4,7 +4,7 @@ import "fmt"
 import "errors"
 
 // Hello returns a greeting for the named person.
-func Hello(name string) string {
+func Hello(name string) (string,error) {
    // If no name was given, return an error with a message.
     if name == "" {
         return "", errors.New("empty name")