fix(checkbox): setting blank aria-label by default (#10281)

Fixes the checkbox adding a blank `aria-label` to the underlying input element by default.

src/lib/checkbox/checkbox.html

@@ -11,7 +11,7 @@
            [attr.name]="name"
            [tabIndex]="tabIndex"
            [indeterminate]="indeterminate"
-           [attr.aria-label]="ariaLabel"
+           [attr.aria-label]="ariaLabel || null"
            [attr.aria-labelledby]="ariaLabelledby"
            [attr.aria-checked]="_getAriaChecked()"
            (change)="_onInteractionEvent($event)"

src/lib/checkbox/checkbox.spec.ts

@@ -701,7 +701,7 @@ describe('MatCheckbox', () => {
     }));
   });
 
-  describe('with provided aria-label ', () => {
+  describe('aria-label ', () => {
     let checkboxDebugElement: DebugElement;
     let checkboxNativeElement: HTMLElement;
     let inputElement: HTMLInputElement;
@@ -715,6 +715,13 @@ describe('MatCheckbox', () => {
       fixture.detectChanges();
       expect(inputElement.getAttribute('aria-label')).toBe('Super effective');
     });
+
+    it('should not set the aria-label attribute if no value is provided', () => {
+      fixture = TestBed.createComponent(SingleCheckbox);
+      fixture.detectChanges();
+
+      expect(fixture.nativeElement.querySelector('input').hasAttribute('aria-label')).toBe(false);
+    });
   });
 
   describe('with provided aria-labelledby ', () => {