我有一个JSON对象，如下所示

[{
"id": 1,
"firstName": "Sam",
"middleName": "poller",
"lastName": "Aniston",
"address": "New York City",
}, {
"id": 2,
"firstName": "Apple",
"middleName": null,
"lastName": "Jolie",
"address": "Beverley Hills",
}, {
"id": 3,
"firstName": "Anna",
"middleName": "mary",
"lastName": "Dobrev",
"address": "London",
}]

我使用selectas在视图中填充此数据，

<div >
  <select  ng-model="invigilator" ng-options="invigilator.id as  (invigilator.firstName+' '+invigilator.middleName+' '+invigilator.lastName) for invigilator in invigilatorList"  ng- click="getinvigilator(invigilator)" class="form-control"> 
                                <option value="">Select Invigilator</option>

                            </select></div>

但我有很多选择，

Sam poller Aniston
Apple null Jolie
Anna mary dobrev

我如何删除中间名中的空值并只显示Apple Jolie。