fix: Lint errors for account username return type

addons/api/addon/models/account.js

@@ -16,11 +16,15 @@ export default class AccountModel extends GeneratedAccountModel {
    * Convenience for getting username in account.
    * @type {string}
    */
-  @computed('attributes')
+  @computed('attributes.{login_name}')
   get username() {
-    if(this.type === 'password') {
-      return this.attributes.login_name;
+    let username = '';
+    switch (this.type) {
+      case 'password':
+        username = this.attributes.login_name;
+        break;
     }
+    return username;
   }
 
   // =methods

addons/api/tests/unit/models/account-test.js

@@ -17,7 +17,7 @@ module('Unit | Model | account', function (hooks) {
       name: 'name',
       type: 'password',
     });
-    assert.equal(model.username, null);
+    assert.notOk(model.username);
     model.attributes.login_name = 'username';
     assert.equal(model.username, 'username');
   });