Following is a dropdown data-bound with AngualarJS:

   <select name="lineCode" class="form-control input-sm"
        ng-model="monitoringProbe.tdmCapture.selectedTDMCard.layer1Properties.lineCode"
        ng-options="l.id as l.name for l in monitoringProbeTDMCaptureData.lineCodes"
                    required >
   </select>

I populate the ng-options as follows:

 virtualServerMonitoringProbeService.comboProperties().query({},{itemType:1, interfaceType: interfaceType}).$promise.then(
            function(result){
                monitoringProbeTDMCaptureData.lineCodes = result;
            },
            function(error){
                messageNotificationFactory.setNotification('error', error.data.message);
            }
        );

According to the following post, when there's no value in ng-model to match the items in the dropdown. Why does AngularJS include an empty option in select?

Therefore I force the first element in the list to be the selected value, as follows:

     virtualServerMonitoringProbeService.comboProperties().query({},{itemType:1, interfaceType: interfaceType}).$promise.then(
            function(result){
                monitoringProbeTDMCaptureData.lineCodes = result;
                tdmCapture.selectedTDMCard.layer1Properties.lineCode = monitoringProbeTDMCaptureData.lineCodes[0];
            },
            function(error){
                messageNotificationFactory.setNotification('error', error.data.message);
            }
        );

But still the dropdown selection is empty. At run time this is how it looks like:

<select name="lineCode" class="form-control input-sm ng-pristine ng-valid ng-valid-required" ng-model="monitoringProbe.tdmCapture.selectedTDMCard.layer1Properties.lineCode" ng-options="l.id as l.name for l in monitoringProbeTDMCaptureData.lineCodes" required="">
   <option value="?" selected="selected"></option>
   <option value="0">AMI</option>
    <option value="1">B8ZS</option>
</select>

Anything wrong with this code?