Duplicate md-option values are not allowed in a select. Duplicate value "" found


#1

Hello, I made md-option but why is it considered duplicate

this my html

<md-input-container md-no-float class="icon-title" >
                <i class="fa fa-edit"></i>
                <md-select name="kaiorigin" required ng-model="ekai.kaiorigin" aria-label="md-option"  style="border-bottom:1px solid #3B3837; width:70%; ">
					
					<md-option value="0" selected="selected">Kota  Awal</md-option>
					
					<md-option ng-repeat="city in kaicity track by $index"  value="{{city.kc_kode}}">{{city.kc_nm}}</md-option>
					
				</md-select>
            </md-input-container>
	
	<md-input-container md-no-float class="icon-title" >
                <i class="fa fa-edit"></i>
                <md-select name="kaidestination" required ng-model="ekai.kaidestination" aria-label="md-option"  style="border-bottom:1px solid #3B3837; width:70%; ">
					
					<md-option value="0" selected="selected">Kota  Tujuan</md-option>
					
					<md-option ng-repeat="city in kaicity " value="{{city.kc_kode}}">{{city.kc_nm}}</md-option>
					
				</md-select>
            </md-input-container>

this my js

 $scope.initialForm = function () {
        //console.log('aaa');
		$ionicHistory.clearCache();
		$ionicHistory.clearHistory();
		$rootScope.dashboard = 1;
        $scope.kaiList = [];
        $scope.ekai = [];
		$scope.offset = 0;
		$scope.limit = 10;
		
		var id = $scope.datauser[0].id;
		apiService.getAll('kaicity',id,0,$scope.offset,$scope.limit).success(function(data) {
			console.log(data);
			$scope.kaicity = data;
			//console.log(data);
		}).finally(function() {
			$scope.$broadcast('scroll.refreshComplete');
		});

and this my console