ClassCastException when converting a project to JPA

[GoogleCodeExporter]

What steps will reproduce the problem?
1. Start with a GAE project
2. Select Project > Properties > Project Facets and check the "JPA" checkbox.  
Click the "Further configuration available..." link to get the advanced dialog 
and add a "Connection" (anything other than "<None>".
3. Click "OK" on both dialogs

What is the expected output? What do you see instead?
Expected successful conversion to a JPA project. Instead a ClassCastException 
is thrown.

Please use labels and text to provide additional information.

This is in both the Kepler and Luna releases (Eclipse 4.3 and 4.4).

Original issue reported on code.google.com by [email protected] on 1 Nov 2014 at 12:08