fix(select): placeholder (empty option) is lost in IE9

Fixes a check inside render for select elements with ngOptions, which compares the selected property of an element with it's desired state.
Ensured the placeholder, if available, is explicitly selected if the model value can not be found in the option list.
Without these fixes it's up to the browser implementation to decide which option to choose.
In most browsers, this has the effect of displaying the first item in the list. In IE9 however, this causes the select to display nothing.

Closes angular#2150, angular#1826

src/ng/directive/select.js

@@ -394,10 +394,6 @@ var selectDirective = ['$compile', '$parse', function($compile,   $parse) {
 
           if (multiple) {
             selectedSet = new HashMap(modelValue);
-          } else if (modelValue === null || nullOption) {
-            // if we are not multiselect, and we are null then we have to add the nullOption
-            optionGroups[''].push({selected:modelValue === null, id:'', label:''});
-            selectedSet = true;
           }
 
           // We now build up the list of options we need (we merge later)
@@ -422,9 +418,14 @@ var selectDirective = ['$compile', '$parse', function($compile,   $parse) {
               selected: selected                   // determine if we should be selected
             });
           }
-          if (!multiple && !selectedSet) {
-            // nothing was selected, we have to insert the undefined item
-            optionGroups[''].unshift({id:'?', label:'', selected:true});
+          if (!multiple) {
+            if (nullOption || modelValue === null) {
+              // insert null option if we have a placeholder, or the model is null
+              optionGroups[''].unshift({id:'', label:'', selected:!selectedSet});
+            } else if (!selectedSet) {
+              // option could not be found, we have to insert the undefined item
+              optionGroups[''].unshift({id:'?', label:'', selected:true});
+            }
           }
 
           // Now we need to update the list of DOM nodes to match the optionGroups we computed above
@@ -468,7 +469,8 @@ var selectDirective = ['$compile', '$parse', function($compile,   $parse) {
                 if (existingOption.id !== option.id) {
                   lastElement.val(existingOption.id = option.id);
                 }
-                if (existingOption.element.selected !== option.selected) {
+                // lastElement.prop('selected') provided by jQuery has side-effects
+                if (lastElement[0].selected !== option.selected) {
                   lastElement.prop('selected', (existingOption.selected = option.selected));
                 }
               } else {

test/ng/directive/selectSpec.js

@@ -977,6 +977,19 @@ describe('select', function() {
         expect(option.attr('id')).toBe('road-runner');
         expect(option.attr('custom-attr')).toBe('custom-attr');
       });
+
+      it('should be selected, if it is available and no other option is selected', function() {
+        // selectedIndex is used here because jqLite incorrectly reports element.val()
+        scope.$apply(function() {
+          scope.values = [{name: 'A'}];
+        });
+        createSingleSelect(true);
+        // ensure the first option (the blank option) is selected
+        expect(element[0].selectedIndex).toEqual(0);
+        scope.$digest();
+        // ensure the option has not changed following the digest
+        expect(element[0].selectedIndex).toEqual(0);
+      });
     });
 
 
@@ -1099,6 +1112,21 @@ describe('select', function() {
         browserTrigger(element, 'change');
         expect(scope.selected).toEqual(['0']);
       });
+
+      it('should deselect all options when model is emptied', function() {
+        createMultiSelect();
+         scope.$apply(function() {
+          scope.values = [{name: 'A'}, {name: 'B'}];
+          scope.selected = [scope.values[0]];
+        });
+        expect(element.find('option')[0].selected).toEqual(true);
+
+        scope.$apply(function() {
+          scope.selected.pop();
+        });
+
+        expect(element.find('option')[0].selected).toEqual(false);
+      })
     });