fix(select): allow for null values in HTML select options bound with ngValue

closes #12829

modules/@angular/forms/src/directives/select_control_value_accessor.ts

@@ -6,13 +6,13 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {Directive, ElementRef, Host, Input, OnDestroy, Optional, Renderer, forwardRef} from '@angular/core';
+import {Directive, ElementRef, Host, Input, OnDestroy, Optional, Provider, Renderer, forwardRef} from '@angular/core';
 
 import {isPrimitive, looseIdentical} from '../facade/lang';
 
 import {ControlValueAccessor, NG_VALUE_ACCESSOR} from './control_value_accessor';
 
-export const SELECT_VALUE_ACCESSOR: any = {
+export const SELECT_VALUE_ACCESSOR: Provider = {
   provide: NG_VALUE_ACCESSOR,
   useExisting: forwardRef(() => SelectControlValueAccessor),
   multi: true
@@ -115,8 +115,8 @@ export class SelectControlValueAccessor implements ControlValueAccessor {
 
   /** @internal */
   _getOptionValue(valueString: string): any {
-    let key: string = _extractId(valueString);
-    return this._optionMap.has(key) ? this._optionMap.get(key) : valueString;
+    const id: string = _extractId(valueString);
+    return this._optionMap.has(id) ? this._optionMap.get(id) : valueString;
   }
 }
 
@@ -158,7 +158,7 @@ export class NgSelectOption implements OnDestroy {
     this._renderer.setElementProperty(this._element.nativeElement, 'value', value);
   }
 
-  ngOnDestroy() {
+  ngOnDestroy(): void {
     if (this._select) {
       this._select._optionMap.delete(this.id);
       this._select.writeValue(this._select.value);

modules/@angular/forms/src/directives/select_multiple_control_value_accessor.ts

@@ -6,13 +6,13 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {Directive, ElementRef, Host, Input, OnDestroy, OpaqueToken, Optional, Renderer, Type, forwardRef} from '@angular/core';
+import {Directive, ElementRef, Host, Input, OnDestroy, Optional, Provider, Renderer, forwardRef} from '@angular/core';
 
 import {isPrimitive, looseIdentical} from '../facade/lang';
 
 import {ControlValueAccessor, NG_VALUE_ACCESSOR} from './control_value_accessor';
 
-export const SELECT_MULTIPLE_VALUE_ACCESSOR = {
+export const SELECT_MULTIPLE_VALUE_ACCESSOR: Provider = {
   provide: NG_VALUE_ACCESSOR,
   useExisting: forwardRef(() => SelectMultipleControlValueAccessor),
   multi: true
@@ -121,8 +121,8 @@ export class SelectMultipleControlValueAccessor implements ControlValueAccessor
 
   /** @internal */
   _getOptionValue(valueString: string): any {
-    let key: string = _extractId(valueString);
-    return this._optionMap.has(key) ? this._optionMap.get(key)._value : valueString;
+    const id: string = _extractId(valueString);
+    return this._optionMap.has(id) ? this._optionMap.get(id)._value : valueString;
   }
 }
 
@@ -180,12 +180,10 @@ export class NgSelectMultipleOption implements OnDestroy {
     this._renderer.setElementProperty(this._element.nativeElement, 'selected', selected);
   }
 
-  ngOnDestroy() {
+  ngOnDestroy(): void {
     if (this._select) {
       this._select._optionMap.delete(this.id);
       this._select.writeValue(this._select.value);
     }
   }
 }
-
-export const SELECT_DIRECTIVES = [SelectMultipleControlValueAccessor, NgSelectMultipleOption];

modules/@angular/forms/test/template_integration_spec.ts

@@ -23,7 +23,7 @@ export function main() {
           NgModelRadioForm, NgModelRangeForm, NgModelSelectForm, NgNoFormComp, InvalidNgModelNoName,
           NgModelOptionsStandalone, NgModelCustomComp, NgModelCustomWrapper,
           NgModelValidationBindings, NgModelMultipleValidators, NgAsyncValidator,
-          NgModelAsyncValidation
+          NgModelAsyncValidation, NgModelSelectWithNullForm
         ],
         imports: [FormsModule]
       });
@@ -699,6 +699,28 @@ export function main() {
            expect(select.nativeElement.value).toEqual('2: Object');
            expect(secondNYC.nativeElement.selected).toBe(true);
          }));
+
+      it('should work with null option', fakeAsync(() => {
+           const fixture = TestBed.createComponent(NgModelSelectWithNullForm);
+           const comp = fixture.componentInstance;
+           comp.cities = [{'name': 'SF'}, {'name': 'NYC'}];
+           comp.selectedCity = null;
+           fixture.detectChanges();
+
+           const select = fixture.debugElement.query(By.css('select'));
+
+           select.nativeElement.value = '2: Object';
+           dispatchEvent(select.nativeElement, 'change');
+           fixture.detectChanges();
+           tick();
+           expect(comp.selectedCity['name']).toEqual('NYC');
+
+           select.nativeElement.value = '0: null';
+           dispatchEvent(select.nativeElement, 'change');
+           fixture.detectChanges();
+           tick();
+           expect(comp.selectedCity).toEqual(null);
+         }));
     });
 
     describe('custom value accessors', () => {
@@ -1078,6 +1100,20 @@ class NgModelSelectForm {
   cities: any[] = [];
 }
 
+@Component({
+  selector: 'ng-model-select-null-form',
+  template: `
+    <select [(ngModel)]="selectedCity">
+      <option *ngFor="let c of cities" [ngValue]="c"> {{c.name}} </option>
+      <option [ngValue]="null">Unspecified</option>
+    </select>
+  `
+})
+class NgModelSelectWithNullForm {
+  selectedCity: {[k: string]: string} = {};
+  cities: any[] = [];
+}
+
 @Component({
   selector: 'ng-model-custom-comp',
   template: `