updated pr with ui-elect master from angular-ui#422

Author: davisford

src/select.js

@@ -873,6 +873,15 @@
         $select.onSelectCallback = $parse(attrs.onSelect);
         $select.onRemoveCallback = $parse(attrs.onRemove);
 
+        // When configured for multiple, override $isEmpty so that ng-required works as expected.
+        if ($select.multiple) {
+          var defaultIsEmptyFn = ngModel.$isEmpty;
+
+          ngModel.$isEmpty = function (value) {
+            return (angular.isArray(value) && value.length === 0) || defaultIsEmptyFn(value);
+          };
+        }
+
         //From view --> model
         ngModel.$parsers.unshift(function (inputValue) {
           var locals = {},

test/select.spec.js

@@ -1553,7 +1553,13 @@ describe('ui-select tests', function() {
 
       expect(el.find('.ui-select-match-item [uis-transclude-append]:not(.ng-hide)').text())
          .toBe("Wladimir <[email protected]>Samantha <[email protected]>Nicole <[email protected]>");
+    });
 
+    it('should be marked invalid when required and empty', function () {
+      scope.selection.selectedMultiple = [];
+      var el = createUiSelectMultiple({required: true});
+      expect(el.scope().$select.ngModel.$invalid).toBe(true);
+      expect(el.scope().$select.ngModel.$error.required).toBe(true);
     });
 
     it('should support multiple="multiple" attribute', function() {