Iron form serialize method always returning undefined on Polymer 2.0

[bmodeprogrammer]

Description

When submit serialize method returns undefined, and the submit function it's called two times;

Expected outcome

{cenas: input}

Actual outcome

undefined

Live Demo

https://jsbin.com/micinalacu/1/edit?html,console,output

Browsers Affected

• Chrome
• Firefox
• Safari 9
• Safari 8
• Safari 7
• Edge
• IE 11
• IE 10

I did not test in another browser.
Stackoverflow question:
http://stackoverflow.com/questions/43075125/iron-form-with-polymer-2-0

[notwaldorf]

There's no method called serialize on iron-form#2.0-preview right now; it's called serializeForm. There was a bug where Polymer had a serialize method, and that was stomping over the form's.

[bmodeprogrammer]

@notwaldorf yah, with the serializeForm works. But why it's called two times? and why I did not receive a run time error trying to execute a non defined method?
here: https://jsbin.com/cowocamimo/1/edit?html,console,output