fix(material/sort): If there is no direction, setting active as empty

src/material/sort/sort.spec.ts

@@ -455,12 +455,18 @@ function testSingleColumnSortDirectionSequence(
   component.matSort.direction = '';
 
   // Run through the sequence to confirm the order
-  const actualSequence = expectedSequence.map(() => {
+  const actualSequence = expectedSequence.map(currentSequence => {
     component.sort(id);
 
     // Check that the sort event's active sort is consistent with the MatSort
-    expect(component.matSort.active).toBe(id);
-    expect(component.latestSortEvent.active).toBe(id);
+    if (currentSequence) {
+      expect(component.matSort.active).toBe(id);
+      expect(component.latestSortEvent.active).toBe(id);
+    } else {
+      // For empty sequence the mat sort active should be empty
+      expect(component.matSort.active).toBe('');
+      expect(component.latestSortEvent.active).toBe('');
+    }
 
     // Check that the sort event's direction is consistent with the MatSort
     expect(component.matSort.direction).toBe(component.latestSortEvent.direction);

src/material/sort/sort.ts

@@ -82,7 +82,7 @@ export class MatSort implements OnChanges, OnDestroy, OnInit {
   readonly _stateChanges = new Subject<void>();
 
   /** The id of the most recently sorted MatSortable. */
-  @Input('matSortActive') active: string;
+  @Input('matSortActive') active: string = '';
 
   /**
    * The direction to set when an MatSortable is initially sorted.
@@ -165,7 +165,9 @@ export class MatSort implements OnChanges, OnDestroy, OnInit {
     } else {
       this.direction = this.getNextSortDirection(sortable);
     }
-
+    if (!this.direction) {
+      this.active = '';
+    }
     this.sortChange.emit({active: this.active, direction: this.direction});
   }