Cannot add to firebase using polymer project's <firebase-element>

Question

I am using polymer's to add records to my firebase. I am able to successfully log in buy cannot write, i get an error:

'Uncaught TypeError: Cannot read property 'ref' of undefined'.

Has any one successfully tried to add record using new firebase-element?

JS Bin is at http://jsbin.com/nohujoceto/edit?html,console,output