Custom and first options in ember-power-select

I'm using Ember-power-select-with-create to make custom selections possible in my dropdowns.

This is the power-select part in the .hbs file.

{{#power-select-multiple-with-create
        options=options //array for prefill values
        selected=offer.offer //is where we save it to (offer is the model and has an array named offer)
        onchange=(action (mut offer.offer)) //default onchange for prefill options
        onfocus=(action "handleFocus")
        onblur=(action "handleBlur")
        oncreate=(action "createOffer" offer.offer) //This calls "createOffer"
        buildSuggestion=suggestion
      as |offer|}}
        {{offer}}
      {{/power-select-multiple-with-create}}

The "createOffer" function in my .js file looks like this:
It gets two values passed: selected which is offer.offer and searchText which is the input that the user is trying to add.

createOffer(selected, searchText)
{
  if (selected == null)
  {
    selected = []; //This is what I'm currently trying: if its null initialize it
  }

  if (selected.includes(searchText)) { //Don't add if it's already added
    this.get('notify').alert("Already added!", { closeAfter: 4000 });
  }
  else { // if it's not yet added push it to the array
    selected.pushObject(searchText);
  }
}

This code works perfectly fine for adding those that we predefined as well for custom options, however it does not work if it is the first and a custom offer that we try to add to a new group of offers.

I'm assuming it has something to do with the fact that the array is not yet initialized. A pointer to the fact that it is due to the array not being initialized is that I get an error message along the lines of: Can't call pushObject on undefined. And I'm assuming the reason that it works with predetermined values is that ember-power-select probably initializes it somewhere but I couldn't find any documentation about it.

Thanks for your answers!

If anyone ever stumbles upon this, this was the solution
Calling that when we create the offer and then initializing the offer array like that:

offer.set('offer', []);