then() returning a null value when it should be pending

Ember 2.17

I am calling an helper from my template :

line, as well as pricing are ember models.

The helper is as following :

import { helper } from '@ember/component/helper';

export function pricingsFullPricing([pricing]) {
  pricing.then(
    p=>{
      debugger
    },p=>{

    }
  )
}
export default helper(pricingsFullPricing);

When I run the page, debugger is called twice (the template loop run once).

First time p is null, the second time it is a pricing.

Isn't then supposed to prevent that? Why does it behave like that?