Ember: change attribute of nullable relationship

I have a model company and a model address. company.address belongs to address. So when I fetch a company record model(params) {return this.store.findRecord('company', params.companyID);}I can access the address attributes with model.address.street. But when my backend retruns address: null because the company dosnt have a relationship with an address and I want that the user can set the street by a input field, I get the error Assertion Failed: Cannot delegate set('street', a) to the 'content' property of object proxy <(subclass of Ember.ObjectProxy):ember1458>: its 'content' is undefined."

Here is the json with the null relationship:

{"data": {
    "attributes": {"name": "test-company"}, "id": "5", 
    "relationships": {
        "address": {
            "data": null
            }
        }, 
        "type": "companies"
    }
}

So how can I avoid this error? I could proof the model.address after fetching the company record if it has an id but doing this in every route isnt really smart.