fix(autocomplete): error when typing in input with disabled autocomplete and no panel

Fixes an edge case where the input will throw an error if it has a disabled autocomplete and no autocomplete panel.

Fixes #11876.

Author: crisbeto

src/lib/autocomplete/autocomplete-trigger.ts

@@ -328,7 +328,7 @@ export class MatAutocompleteTrigger implements ControlValueAccessor, OnDestroy {
       this.activeOption._selectViaInteraction();
       this._resetActiveItem();
       event.preventDefault();
-    } else {
+    } else if (this.autocomplete) {
       const prevActiveItem = this.autocomplete._keyManager.activeItem;
       const isArrowKey = keyCode === UP_ARROW || keyCode === DOWN_ARROW;
 

src/lib/autocomplete/autocomplete.spec.ts

@@ -522,6 +522,16 @@ describe('MatAutocomplete', () => {
     expect(boundingBox.getAttribute('dir')).toEqual('ltr');
   });
 
+  it('should not throw when typing in an element with a null and disabled autocomplete', () => {
+    const fixture = createComponent(InputWithoutAutocompleteAndDisabled);
+    fixture.detectChanges();
+
+    expect(() => {
+      dispatchKeyboardEvent(fixture.nativeElement.querySelector('input'), 'keydown', SPACE);
+      fixture.detectChanges();
+    }).not.toThrow();
+  });
+
   describe('forms integration', () => {
     let fixture: ComponentFixture<SimpleAutocomplete>;
     let input: HTMLInputElement;
@@ -2377,3 +2387,10 @@ class AutocompleteWithDifferentOrigin {
   selectedValue: string;
   values = ['one', 'two', 'three'];
 }
+
+
+@Component({
+  template: '<input [matAutocomplete]="null" matAutocompleteDisabled>'
+})
+class InputWithoutAutocompleteAndDisabled {
+}