Edit in JSFiddle

var myApp = angular.module('myApp', []);

myApp.controller('MainCtrl', ['$scope', function ($scope) {

    $scope.main = {};
    
    // No data
    $scope.main.test1 = [];
    
    // We have data!
    $scope.main.test2 = [{
        "some": "data"
    }];
    
}]);

<div ng-app="myApp">
    <div ng-controller="MainCtrl">
        <p>Test 1: {{ main.test1.length > 0 && 'My data' || 'No data' }}</p>
        <p>Test 2: {{ main.test2.length > 0 && 'My data' || 'No data' }}</p>
    </div>
</div>