Sometimes, you don't know if the value is set or not. That's what defaults are for.
I use this when I need to make sure a variable has some value. You can set it in your controller
$scope.possiblyEmptyVariable = $scope.possiblyEmptyVariable || "default value";
Works great without Angular as well
// some object that may or may not have a property 'x' set
var data = {};
// Set default value of "default"
// carefull, values like 'null', false, 0 will still fall to defaults
data.x = data.x || "default";
// Set default value of "default"
// this will not fall to defaults on values like 'null', false, 0
data.x = !"x" in data || "default";
If you need to set a bunch of values, use angular.extend or jQuery.extend
data.z = "value already set";
var defaults = { x: "default", y: 1, z: "default" };
var newData = angular.extend({}, defaults, data);
// { x: "default, y: 1, z: "value already set" }
Hope that helps
$scope.your_model_name_here = ''