Minor cleanup around cloning methods

src/sprites/rendered-target.js

@@ -582,7 +582,7 @@ RenderedTarget.prototype.goBackLayers = function (nLayers) {
 
 /**
  * Move behind some other rendered target.
- * @param {!Clone} other Other rendered target to move behind.
+ * @param {!RenderedTarget} other Other rendered target to move behind.
  */
 RenderedTarget.prototype.goBehindOther = function (other) {
     if (this.renderer) {
@@ -637,11 +637,11 @@ RenderedTarget.prototype.keepInFence = function (newX, newY, optFence) {
 /**
  * Make a clone, copying any run-time properties.
  * If we've hit the global clone limit, returns null.
- * @return {!RenderedTarget} New clone.
+ * @return {RenderedTarget} New clone.
  */
 RenderedTarget.prototype.makeClone = function () {
     if (!this.runtime.clonesAvailable() || this.isStage) {
-        return; // Hit max clone limit, or this is the stage.
+        return null; // Hit max clone limit, or this is the stage.
     }
     this.runtime.changeCloneCounter(1);
     var newClone = this.sprite.createClone();

src/sprites/sprite.js

@@ -46,7 +46,7 @@ var Sprite = function (blocks, runtime) {
 
 /**
  * Create a clone of this sprite.
- * @returns {!Clone} Newly created clone.
+ * @returns {!RenderedTarget} Newly created clone.
  */
 Sprite.prototype.createClone = function () {
     var newClone = new RenderedTarget(this, this.runtime);