title: EmberJS Data Assert in setRecordDataFor "Illegal set of identifier"
body: <p>Using 3.28 I am hitting an <a href="https://github.com/emberjs/data/blob/9889ebbd4eec162dba17bb00126ee71e49d04bce/packages/store/addon/-private/system/record-data-for.ts#L31" rel="noreferrer">assert deep inside Ember Data</a> when retrieving a relationship on one of my models. I can run the following query just fine:</p>
  <pre><code>return this.store.findRecord('project', project_id)
  </code></pre>
  <p>However when I run a subsequent</p>
  <pre><code>const monitors = await model.monitors;
  </code></pre>
  <p>in my afterModel() of the route, this assert is triggered.</p>
  <p>My Models look pretty standard:</p>
  <pre><code>export default class ProjectModel extends Model {
    @attr('string') name;
    @belongsTo('user') creator;
    @attr('date') created;
    @attr('date') changed;
    @hasMany('domain-monitor') monitors;
  }
  
  export default class DomainMonitorModel extends Model {
    @belongsTo('project') project;
    @hasMany('page-monitor') pages;
    @attr('string') protocol;
    @attr('string') domain;
    @attr('date') created;
    @attr('date') changed;
  }
  </code></pre>
  <p>If someone can point to what is going wrong, I am happy to submit an MR to improve this assert message to hopefully unstuck someone in the future. Thanks!</p>