URL Rewriter: new rules can be saved without selecting a type

Note that this issue only applies to version 1.04.01 of the Url Rewriter.

This behavior can be reproduced through the following steps:

1. Run the url rewriter demo 1.04.01;
2. Create a new Url rewriter rule (note that there is only one mandatory field called Type: do not choose any type);
3. Save & close.

Current behavior: The document is saved.

Expected behavior: The document should not be saved and should show an error to choose a Type.