Fix TS 2.7 error

Author: jelbourn

src/lib/table/table-data-source.ts

@@ -8,8 +8,9 @@
 
 import {DataSource} from '@angular/cdk/table';
 import {BehaviorSubject} from 'rxjs/BehaviorSubject';
-import {MatPaginator} from '@angular/material/paginator';
-import {MatSort} from '@angular/material/sort';
+import {Observable} from 'rxjs/Observable';
+import {MatPaginator, PageEvent} from '@angular/material/paginator';
+import {MatSort, Sort} from '@angular/material/sort';
 import {Subscription} from 'rxjs/Subscription';
 import {combineLatest} from 'rxjs/operators/combineLatest';
 import {map} from 'rxjs/operators/map';
@@ -178,8 +179,9 @@ export class MatTableDataSource<T> extends DataSource<T> {
   _updateChangeSubscription() {
     // Sorting and/or pagination should be watched if MatSort and/or MatPaginator are provided.
     // Otherwise, use an empty observable stream to take their place.
-    const sortChange = this._sort ? this._sort.sortChange : empty();
-    const pageChange = this._paginator ? this._paginator.page : empty();
+    const sortChange = (this._sort ? this._sort.sortChange : empty()) as Observable<Sort | null>;
+    const pageChange =
+        (this._paginator ? this._paginator.page : empty()) as Observable<PageEvent | null>;
 
     if (this._renderChangesSubscription) {
       this._renderChangesSubscription.unsubscribe();
@@ -190,10 +192,10 @@ export class MatTableDataSource<T> extends DataSource<T> {
       combineLatest(this._filter),
       map(([data]) => this._filterData(data)),
       // Watch for filtered data or sort changes to provide an ordered set of data.
-      combineLatest(sortChange.pipe(startWith(null!))),
+      combineLatest(sortChange.pipe(startWith(null))),
       map(([data]) => this._orderData(data)),
       // Watch for ordered data or page changes to provide a paged set of data.
-      combineLatest(pageChange.pipe(startWith(null!))),
+      combineLatest(pageChange.pipe(startWith(null))),
       map(([data]) => this._pageData(data))
     )
     // Watched for paged data changes and send the result to the table to render.