Remove goog.isNull in interaction classes

src/ol/interaction/dragpaninteraction.js

@@ -77,7 +77,7 @@ ol.interaction.DragPan.handleDragEvent_ = function(mapBrowserEvent) {
   if (this.kinetic_) {
     this.kinetic_.update(centroid[0], centroid[1]);
   }
-  if (!goog.isNull(this.lastCentroid)) {
+  if (this.lastCentroid) {
     var deltaX = this.lastCentroid[0] - centroid[0];
     var deltaY = centroid[1] - this.lastCentroid[1];
     var map = mapBrowserEvent.map;
@@ -145,7 +145,7 @@ ol.interaction.DragPan.handleDownEvent_ = function(mapBrowserEvent) {
       view.setHint(ol.ViewHint.INTERACTING, 1);
     }
     map.render();
-    if (!goog.isNull(this.kineticPreRenderFn_) &&
+    if (this.kineticPreRenderFn_ &&
         map.removePreRenderFunction(this.kineticPreRenderFn_)) {
       view.setCenter(mapBrowserEvent.frameState.viewState.center);
       this.kineticPreRenderFn_ = null;