Ember action passing null

I have the following:

Two models belonging to each other

export default DS.Model.extend({    
            cv: DS.belongsTo('cv'),

export default DS.Model.extend({  
            title: DS.attr('string'),
            personalDetail: DS.belongsTo('personal-detail'),

and a route with the following

import Ember from 'ember';

export default Ember.Route.extend({
    model() {
        return this.modelFor('build').get('personalDetail'); 
},
    actions: {
        saveDetails(mod)
        {
            const details = this.modelFor('build').get('personalDetail');

        }
    }
});

In the Hbs

  <div class="row">
        <div class="col-xs-2 col-xs-offset-9">
            <button {{action "saveDetails" model on="mouseUp"}} class="btn1 btn--white-blue big right">
                NEXT
                <span>
                    <svg role="img" fill="currentColor">
                        <use xlink:href="icons/icons.svg#arrow-down"></use>
                    </svg>
                </span>     
            </button>
        </div>
    </div>

So what happens here is that I have a root object called cv and has a belongs to relationship to persontalDetail

when I call the info route it gets the model for the build route(which is a parent route) which is the cv object, from there it gets ther personalDetail model and passes it on to the page.

When I click on the savedetails I'm expecting the model to be returned to the method but for some reason a null is being passed.

I have a similar setup on other pages for objects with a has many relationship but I cant get it to work with the above.

Any ideas on what I am doing wrong?