fix(core): resolve compilation errors for latest Typescript 1.9 (#624)

Author: vikerman

src/core/overlay/position/connected-position-strategy.ts

@@ -68,14 +68,14 @@ export class ConnectedPositionStrategy implements PositionStrategy {
       // If the overlay in the calculated position fits on-screen, put it there and we're done.
       if (this._willOverlayFitWithinViewport(overlayPoint, overlayRect, viewportRect)) {
         this._setElementPosition(element, overlayPoint);
-        return Promise.resolve();
+        return Promise.resolve(null);
       }
     }
 
     // TODO(jelbourn): fallback behavior for when none of the preferred positions fit on-screen.
     // For now, just stick it in the first position and let it go off-screen.
     this._setElementPosition(element, firstOverlayPoint);
-    return Promise.resolve();
+    return Promise.resolve(null);
   }
 
   withFallbackPosition(

src/core/overlay/position/global-position-strategy.ts

@@ -103,7 +103,7 @@ export class GlobalPositionStrategy implements PositionStrategy {
 
     applyCssTransform(element, `${tranlateX} ${translateY}`);
 
-    return Promise.resolve();
+    return Promise.resolve(null);
   }
 
   /** Reduce a list of translate values to a string that can be used in the transform property */

src/core/portal/portal-directives.ts

@@ -90,7 +90,7 @@ export class PortalHostDirective extends BasePortalHost {
 
   /** Detatches the currently attached Portal (if there is one) and attaches the given Portal. */
   private _replaceAttachedPortal(p: Portal<any>): void {
-    let maybeDetach = this.hasAttached() ? this.detach() : Promise.resolve();
+    let maybeDetach = this.hasAttached() ? this.detach() : Promise.resolve(null);
 
     maybeDetach.then(() => {
       if (p != null) {