No Error Message When Adding a Non-exisitng User To a Group

When adding a user to a group, it doesn't show an error message if the user doesn't exist.

Example:
In previous versions of Confluence 3.3.3, the costumer tried to add a non-existing user to a group he would receive the following error message: "The following error(s) occurred: User xyz123 could not be found. Please confirm his or her existence with a Confluence Administrator."