ember data not populating model errors

jobs_new_controller.js

// using ActiveModelAdapter
App.ApplicationAdapter = DS.ActiveModelAdapter.extend();

// simple model
App.Job = DS.Model.extend({
  external_ref: DS.attr("string")
});

// creating a new Job. 
App.JobsNewController = Ember.Controller.extend({
  actions: {
    save: function() {
      var newJob = this.store.createRecord('job', {
        'external_ref' : this.external_ref,
      });

      
      newJob.save().then(function(){

      }, function(fail){
        // server fails validation, so responds to save with {"errors":{"external_ref":["can't be blank"]}}

        // InvalidError object
        console.log(fail)

        // this is the obj sent from server
        console.log(fail.errors)

        // an ember array of length 0
        console.log(newJob.get('errors').toArray())

      });
    }
  }
});

new.hbs

{{!-- jobs/new.hbs --}}

{{#if errors.length}}
  There has been an error
{{/if}}


{{input type="text" value=external_ref placeholder='External ref' class="form-control"  }}

<button {{action 'save'}}>Save</button>