diff --git a/src/ol/Disposable.js b/src/ol/Disposable.js
index 633e2017aa..b3d9ee28ac 100644
--- a/src/ol/Disposable.js
+++ b/src/ol/Disposable.js
@@ -1,7 +1,7 @@
 /**
  * @module ol/Disposable
  */
-import {nullFunction} from './index.js';
+import {UNDEFINED} from './functions.js';
 
 /**
  * Objects that need to clean up after themselves.
@@ -30,5 +30,5 @@ Disposable.prototype.dispose = function() {
  * Extension point for disposable objects.
  * @protected
  */
-Disposable.prototype.disposeInternal = nullFunction;
+Disposable.prototype.disposeInternal = UNDEFINED;
 export default Disposable;
diff --git a/src/ol/View.js b/src/ol/View.js
index 826bbb55dd..b8e473e5e9 100644
--- a/src/ol/View.js
+++ b/src/ol/View.js
@@ -2,7 +2,8 @@
  * @module ol/View
  */
 import {DEFAULT_TILE_SIZE} from './tilegrid/common.js';
-import {inherits, getUid, nullFunction} from './index.js';
+import {inherits, getUid} from './index.js';
+import {UNDEFINED} from './functions.js';
 import {createExtent, none as centerNone} from './centerconstraint.js';
 import BaseObject from './Object.js';
 import {createSnapToResolutions, createSnapToPower} from './resolutionconstraint.js';
@@ -948,7 +949,7 @@ View.prototype.fit = function(geometryOrExtent, opt_options) {
   const centerX = centerRotX * cosAngle - centerRotY * sinAngle;
   const centerY = centerRotY * cosAngle + centerRotX * sinAngle;
   const center = [centerX, centerY];
-  const callback = options.callback ? options.callback : nullFunction;
+  const callback = options.callback ? options.callback : UNDEFINED;
 
   if (options.duration !== undefined) {
     this.animate({
diff --git a/src/ol/control/Control.js b/src/ol/control/Control.js
index d8207029a0..adfaa865ec 100644
--- a/src/ol/control/Control.js
+++ b/src/ol/control/Control.js
@@ -1,7 +1,8 @@
 /**
  * @module ol/control/Control
  */
-import {inherits, nullFunction} from '../index.js';
+import {inherits} from '../index.js';
+import {UNDEFINED} from '../functions.js';
 import MapEventType from '../MapEventType.js';
 import BaseObject from '../Object.js';
 import {removeNode} from '../dom.js';
@@ -67,7 +68,7 @@ const Control = function(options) {
   /**
    * @type {function(ol.MapEvent)}
    */
-  this.render = options.render ? options.render : nullFunction;
+  this.render = options.render ? options.render : UNDEFINED;
 
   if (options.target) {
     this.setTarget(options.target);
@@ -118,7 +119,7 @@ Control.prototype.setMap = function(map) {
     const target = this.target_ ?
       this.target_ : map.getOverlayContainerStopEvent();
     target.appendChild(this.element);
-    if (this.render !== nullFunction) {
+    if (this.render !== UNDEFINED) {
       this.listenerKeys.push(listen(map,
         MapEventType.POSTRENDER, this.render, this));
     }
diff --git a/src/ol/events/EventTarget.js b/src/ol/events/EventTarget.js
index e304322d43..1823574e9d 100644
--- a/src/ol/events/EventTarget.js
+++ b/src/ol/events/EventTarget.js
@@ -1,9 +1,10 @@
 /**
  * @module ol/events/EventTarget
  */
-import {inherits, nullFunction} from '../index.js';
+import {inherits} from '../index.js';
 import Disposable from '../Disposable.js';
 import {unlistenAll} from '../events.js';
+import {UNDEFINED} from '../functions.js';
 import Event from '../events/Event.js';
 
 /**
@@ -96,7 +97,7 @@ EventTarget.prototype.dispatchEvent = function(event) {
       let pendingRemovals = this.pendingRemovals_[type];
       delete this.pendingRemovals_[type];
       while (pendingRemovals--) {
-        this.removeEventListener(type, nullFunction);
+        this.removeEventListener(type, UNDEFINED);
       }
       delete this.dispatching_[type];
     }
@@ -147,7 +148,7 @@ EventTarget.prototype.removeEventListener = function(type, listener) {
     const index = listeners.indexOf(listener);
     if (type in this.pendingRemovals_) {
       // make listener a no-op, and remove later in #dispatchEvent()
-      listeners[index] = nullFunction;
+      listeners[index] = UNDEFINED;
       ++this.pendingRemovals_[type];
     } else {
       listeners.splice(index, 1);
diff --git a/src/ol/featureloader.js b/src/ol/featureloader.js
index 14411cf176..08a7baf0a3 100644
--- a/src/ol/featureloader.js
+++ b/src/ol/featureloader.js
@@ -1,7 +1,7 @@
 /**
  * @module ol/featureloader
  */
-import {nullFunction} from './index.js';
+import {UNDEFINED} from './functions.js';
 import FormatType from './format/FormatType.js';
 import {parse} from './xml.js';
 
@@ -88,11 +88,11 @@ export function loadFeaturesXhr(url, format, success, failure) {
 export function xhr(url, format) {
   return loadFeaturesXhr(url, format,
     /**
-       * @param {Array.<ol.Feature>} features The loaded features.
-       * @param {ol.proj.Projection} dataProjection Data projection.
-       * @this {ol.source.Vector}
-       */
+     * @param {Array.<ol.Feature>} features The loaded features.
+     * @param {ol.proj.Projection} dataProjection Data projection.
+     * @this {ol.source.Vector}
+     */
     function(features, dataProjection) {
       this.addFeatures(features);
-    }, /* FIXME handle error */ nullFunction);
+    }, /* FIXME handle error */ UNDEFINED);
 }
diff --git a/src/ol/functions.js b/src/ol/functions.js
index dba014d1e0..0850ce61b5 100644
--- a/src/ol/functions.js
+++ b/src/ol/functions.js
@@ -17,3 +17,10 @@ export function TRUE() {
 export function FALSE() {
   return false;
 }
+
+/**
+ * A reusable function, used e.g. as a default for callbacks.
+ *
+ * @return {undefined} Nothing.
+ */
+export function UNDEFINED() {}
diff --git a/src/ol/index.js b/src/ol/index.js
index b64bdd8289..9c7c3e603a 100644
--- a/src/ol/index.js
+++ b/src/ol/index.js
@@ -93,14 +93,6 @@ export function inherits(childCtor, parentCtor) {
 }
 
 
-/**
- * A reusable function, used e.g. as a default for callbacks.
- *
- * @return {undefined} Nothing.
- */
-export function nullFunction() {}
-
-
 /**
  * Counter for getUid.
  * @type {number}
diff --git a/src/ol/interaction/DragBox.js b/src/ol/interaction/DragBox.js
index ff50216601..255482a011 100644
--- a/src/ol/interaction/DragBox.js
+++ b/src/ol/interaction/DragBox.js
@@ -3,8 +3,9 @@
  */
 // FIXME draw drag box
 import Event from '../events/Event.js';
-import {inherits, nullFunction} from '../index.js';
+import {inherits} from '../index.js';
 import {always, mouseOnly, mouseActionButton} from '../events/condition.js';
+import {UNDEFINED} from '../functions.js';
 import PointerInteraction from '../interaction/Pointer.js';
 import RenderBox from '../render/Box.js';
 
@@ -182,7 +183,7 @@ DragBox.prototype.getGeometry = function() {
  * @param {ol.MapBrowserEvent} mapBrowserEvent Map browser event.
  * @protected
  */
-DragBox.prototype.onBoxEnd = nullFunction;
+DragBox.prototype.onBoxEnd = UNDEFINED;
 
 
 /**
diff --git a/src/ol/interaction/Pointer.js b/src/ol/interaction/Pointer.js
index 5f3cbd96be..00981d061f 100644
--- a/src/ol/interaction/Pointer.js
+++ b/src/ol/interaction/Pointer.js
@@ -1,8 +1,8 @@
 /**
  * @module ol/interaction/Pointer
  */
-import {inherits, nullFunction} from '../index.js';
-import {FALSE} from '../functions.js';
+import {inherits} from '../index.js';
+import {FALSE, UNDEFINED} from '../functions.js';
 import MapBrowserEventType from '../MapBrowserEventType.js';
 import MapBrowserPointerEvent from '../MapBrowserPointerEvent.js';
 import Interaction from '../interaction/Interaction.js';
@@ -13,7 +13,7 @@ import {getValues} from '../obj.js';
  * @param {ol.MapBrowserPointerEvent} mapBrowserEvent Event.
  * @this {ol.interaction.Pointer}
  */
-const handleDragEvent = nullFunction;
+const handleDragEvent = UNDEFINED;
 
 
 /**
@@ -36,7 +36,7 @@ const handleDownEvent = FALSE;
  * @param {ol.MapBrowserPointerEvent} mapBrowserEvent Event.
  * @this {ol.interaction.Pointer}
  */
-const handleMoveEvent = nullFunction;
+const handleMoveEvent = UNDEFINED;
 
 
 /**
diff --git a/src/ol/render/Feature.js b/src/ol/render/Feature.js
index aae1cc60ee..1a0541f175 100644
--- a/src/ol/render/Feature.js
+++ b/src/ol/render/Feature.js
@@ -1,7 +1,7 @@
 /**
  * @module ol/render/Feature
  */
-import {nullFunction} from '../index.js';
+import {UNDEFINED} from '../functions.js';
 import {extend} from '../array.js';
 import {createOrUpdateFromCoordinate, createOrUpdateFromFlatCoordinates, getCenter, getHeight} from '../extent.js';
 import GeometryType from '../geom/GeometryType.js';
@@ -244,7 +244,7 @@ RenderFeature.prototype.getStride = function() {
 /**
  * @return {undefined}
  */
-RenderFeature.prototype.getStyleFunction = nullFunction;
+RenderFeature.prototype.getStyleFunction = UNDEFINED;
 
 
 /**
diff --git a/src/ol/render/canvas/Replay.js b/src/ol/render/canvas/Replay.js
index f3253383d3..afa467d860 100644
--- a/src/ol/render/canvas/Replay.js
+++ b/src/ol/render/canvas/Replay.js
@@ -1,7 +1,8 @@
 /**
  * @module ol/render/canvas/Replay
  */
-import {getUid, inherits, nullFunction} from '../../index.js';
+import {getUid, inherits} from '../../index.js';
+import {UNDEFINED} from '../../functions.js';
 import {equals, reverseSubArray} from '../../array.js';
 import {asColorLike} from '../../colorlike.js';
 import {buffer, clone, coordinateRelationship, createEmpty, createOrUpdate,
@@ -1068,7 +1069,7 @@ CanvasReplay.prototype.endGeometry = function(geometry, feature) {
 /**
  * FIXME empty description for jsdoc
  */
-CanvasReplay.prototype.finish = nullFunction;
+CanvasReplay.prototype.finish = UNDEFINED;
 
 
 /**
diff --git a/src/ol/renderer/Layer.js b/src/ol/renderer/Layer.js
index bb64ce9e79..492c5ef242 100644
--- a/src/ol/renderer/Layer.js
+++ b/src/ol/renderer/Layer.js
@@ -1,13 +1,13 @@
 /**
  * @module ol/renderer/Layer
  */
-import {getUid, inherits, nullFunction} from '../index.js';
+import {getUid, inherits} from '../index.js';
 import ImageState from '../ImageState.js';
 import Observable from '../Observable.js';
 import TileState from '../TileState.js';
 import {listen} from '../events.js';
 import EventType from '../events/EventType.js';
-import {FALSE} from '../functions.js';
+import {FALSE, UNDEFINED} from '../functions.js';
 import SourceState from '../source/State.js';
 
 /**
@@ -42,7 +42,7 @@ inherits(LayerRenderer, Observable);
  * @return {T|undefined} Callback result.
  * @template S,T
  */
-LayerRenderer.prototype.forEachFeatureAtCoordinate = nullFunction;
+LayerRenderer.prototype.forEachFeatureAtCoordinate = UNDEFINED;
 
 
 /**
diff --git a/src/ol/renderer/Map.js b/src/ol/renderer/Map.js
index e4aaf05695..6aac6da47c 100644
--- a/src/ol/renderer/Map.js
+++ b/src/ol/renderer/Map.js
@@ -1,12 +1,12 @@
 /**
  * @module ol/renderer/Map
  */
-import {getUid, inherits, nullFunction} from '../index.js';
+import {getUid, inherits} from '../index.js';
 import Disposable from '../Disposable.js';
 import {listen, unlistenByKey} from '../events.js';
 import EventType from '../events/EventType.js';
 import {getWidth} from '../extent.js';
-import {TRUE} from '../functions.js';
+import {TRUE, UNDEFINED} from '../functions.js';
 import {visibleAtResolution} from '../layer/Layer.js';
 import {getLayerRendererPlugins} from '../plugins.js';
 import {iconImageCache} from '../style.js';
@@ -289,7 +289,7 @@ MapRenderer.prototype.removeLayerRendererByKey_ = function(layerKey) {
  * Render.
  * @param {?olx.FrameState} frameState Frame state.
  */
-MapRenderer.prototype.renderFrame = nullFunction;
+MapRenderer.prototype.renderFrame = UNDEFINED;
 
 
 /**
diff --git a/src/ol/renderer/canvas/IntermediateCanvas.js b/src/ol/renderer/canvas/IntermediateCanvas.js
index f2ff25a5a4..2193b8ed72 100644
--- a/src/ol/renderer/canvas/IntermediateCanvas.js
+++ b/src/ol/renderer/canvas/IntermediateCanvas.js
@@ -1,10 +1,11 @@
 /**
  * @module ol/renderer/canvas/IntermediateCanvas
  */
-import {inherits, nullFunction} from '../../index.js';
+import {inherits} from '../../index.js';
 import {scale as scaleCoordinate} from '../../coordinate.js';
 import {createCanvasContext2D} from '../../dom.js';
 import {containsExtent, intersects} from '../../extent.js';
+import {UNDEFINED} from '../../functions.js';
 import CanvasLayerRenderer from '../canvas/Layer.js';
 import {create as createTransform, apply as applyTransform} from '../../transform.js';
 
@@ -123,7 +124,7 @@ IntermediateCanvasRenderer.prototype.forEachLayerAtCoordinate = function(coordin
     return undefined;
   }
 
-  if (this.getLayer().getSource().forEachFeatureAtCoordinate !== nullFunction) {
+  if (this.getLayer().getSource().forEachFeatureAtCoordinate !== UNDEFINED) {
     // for ImageCanvas sources use the original hit-detection logic,
     // so that for example also transparent polygons are detected
     return CanvasLayerRenderer.prototype.forEachLayerAtCoordinate.apply(this, arguments);
diff --git a/src/ol/renderer/webgl/ImageLayer.js b/src/ol/renderer/webgl/ImageLayer.js
index 9f46e75ddd..60522eed4c 100644
--- a/src/ol/renderer/webgl/ImageLayer.js
+++ b/src/ol/renderer/webgl/ImageLayer.js
@@ -2,7 +2,8 @@
  * @module ol/renderer/webgl/ImageLayer
  */
 import {ENABLE_RASTER_REPROJECTION} from '../../reproj/common.js';
-import {inherits, nullFunction} from '../../index.js';
+import {inherits} from '../../index.js';
+import {UNDEFINED} from '../../functions.js';
 import LayerType from '../../LayerType.js';
 import ViewHint from '../../ViewHint.js';
 import {createCanvasContext2D} from '../../dom.js';
@@ -254,7 +255,7 @@ WebGLImageLayerRenderer.prototype.forEachLayerAtPixel = function(pixel, frameSta
     return undefined;
   }
 
-  if (this.getLayer().getSource().forEachFeatureAtCoordinate !== nullFunction) {
+  if (this.getLayer().getSource().forEachFeatureAtCoordinate !== UNDEFINED) {
     // for ImageCanvas sources use the original hit-detection logic,
     // so that for example also transparent polygons are detected
     const coordinate = applyTransform(
diff --git a/src/ol/source/Source.js b/src/ol/source/Source.js
index b466290e0f..495d4028bd 100644
--- a/src/ol/source/Source.js
+++ b/src/ol/source/Source.js
@@ -1,7 +1,8 @@
 /**
  * @module ol/source/Source
  */
-import {inherits, nullFunction} from '../index.js';
+import {inherits} from '../index.js';
+import {UNDEFINED} from '../functions.js';
 import BaseObject from '../Object.js';
 import {get as getProjection} from '../proj.js';
 import SourceState from '../source/State.js';
@@ -89,7 +90,7 @@ Source.prototype.adaptAttributions_ = function(attributionLike) {
  * @return {T|undefined} Callback result.
  * @template T
  */
-Source.prototype.forEachFeatureAtCoordinate = nullFunction;
+Source.prototype.forEachFeatureAtCoordinate = UNDEFINED;
 
 
 /**
diff --git a/src/ol/source/Tile.js b/src/ol/source/Tile.js
index 232b23c89f..a24109f923 100644
--- a/src/ol/source/Tile.js
+++ b/src/ol/source/Tile.js
@@ -1,7 +1,8 @@
 /**
  * @module ol/source/Tile
  */
-import {inherits, nullFunction} from '../index.js';
+import {inherits} from '../index.js';
+import {UNDEFINED} from '../functions.js';
 import TileCache from '../TileCache.js';
 import TileState from '../TileState.js';
 import Event from '../events/Event.js';
@@ -303,7 +304,7 @@ TileSource.prototype.refresh = function() {
  * @param {number} y Tile coordinate y.
  * @param {ol.proj.Projection} projection Projection.
  */
-TileSource.prototype.useTile = nullFunction;
+TileSource.prototype.useTile = UNDEFINED;
 
 
 /**
diff --git a/src/ol/source/Vector.js b/src/ol/source/Vector.js
index 5479cc65c2..5189ebf2f8 100644
--- a/src/ol/source/Vector.js
+++ b/src/ol/source/Vector.js
@@ -2,7 +2,7 @@
  * @module ol/source/Vector
  */
 
-import {getUid, inherits, nullFunction} from '../index.js';
+import {getUid, inherits} from '../index.js';
 import Collection from '../Collection.js';
 import CollectionEventType from '../CollectionEventType.js';
 import ObjectEventType from '../ObjectEventType.js';
@@ -13,7 +13,7 @@ import Event from '../events/Event.js';
 import EventType from '../events/EventType.js';
 import {containsExtent, equals} from '../extent.js';
 import {xhr} from '../featureloader.js';
-import {TRUE} from '../functions.js';
+import {TRUE, UNDEFINED} from '../functions.js';
 import {all as allStrategy} from '../loadingstrategy.js';
 import {isEmpty, getValues} from '../obj.js';
 import Source from '../source/Source.js';
@@ -75,7 +75,7 @@ const VectorSource = function(opt_options) {
    * @private
    * @type {ol.FeatureLoader}
    */
-  this.loader_ = nullFunction;
+  this.loader_ = UNDEFINED;
 
   /**
    * @private
diff --git a/src/ol/style/AtlasManager.js b/src/ol/style/AtlasManager.js
index 81df116720..d3e9ee0239 100644
--- a/src/ol/style/AtlasManager.js
+++ b/src/ol/style/AtlasManager.js
@@ -1,7 +1,8 @@
 /**
  * @module ol/style/AtlasManager
  */
-import {WEBGL_MAX_TEXTURE_SIZE, nullFunction} from '../index.js';
+import {WEBGL_MAX_TEXTURE_SIZE} from '../index.js';
+import {UNDEFINED} from '../functions.js';
 import Atlas from '../style/Atlas.js';
 
 
@@ -180,7 +181,7 @@ AtlasManager.prototype.add = function(id, width, height,
   // the hit-detection atlas, to make sure that the offset is the same for
   // the original image and the hit-detection image.
   const renderHitCallback = opt_renderHitCallback !== undefined ?
-    opt_renderHitCallback : nullFunction;
+    opt_renderHitCallback : UNDEFINED;
 
   const hitInfo = /** @type {ol.AtlasInfo} */ (this.add_(true,
     id, width, height, renderHitCallback, opt_this));
diff --git a/test/spec/ol/renderer/vector.test.js b/test/spec/ol/renderer/vector.test.js
index e66cf9a80c..b38a8dc6d5 100644
--- a/test/spec/ol/renderer/vector.test.js
+++ b/test/spec/ol/renderer/vector.test.js
@@ -1,4 +1,4 @@
-import {nullFunction} from '../../../../src/ol/index.js';
+import {UNDEFINED} from '../../../../src/ol/functions.js';
 import {getListeners} from '../../../../src/ol/events.js';
 import LineString from '../../../../src/ol/geom/LineString.js';
 import Point from '../../../../src/ol/geom/Point.js';
@@ -77,7 +77,7 @@ describe('ol.renderer.vector', function() {
         const imageReplay = replayGroup.getReplay(
           style.getZIndex(), 'Image');
         const setImageStyleSpy = sinon.spy(imageReplay, 'setImageStyle');
-        const drawPointSpy = sinon.stub(imageReplay, 'drawPoint').callsFake(nullFunction);
+        const drawPointSpy = sinon.stub(imageReplay, 'drawPoint').callsFake(UNDEFINED);
         renderFeature(replayGroup, feature,
           style, squaredTolerance, listener, listenerThis);
         expect(setImageStyleSpy.called).to.be(false);
@@ -90,7 +90,7 @@ describe('ol.renderer.vector', function() {
         const imageReplay = replayGroup.getReplay(
           style.getZIndex(), 'Image');
         const setImageStyleSpy = sinon.spy(imageReplay, 'setImageStyle');
-        const drawMultiPointSpy = sinon.stub(imageReplay, 'drawMultiPoint').callsFake(nullFunction);
+        const drawMultiPointSpy = sinon.stub(imageReplay, 'drawMultiPoint').callsFake(UNDEFINED);
         renderFeature(replayGroup, feature,
           style, squaredTolerance, listener, listenerThis);
         expect(setImageStyleSpy.called).to.be(false);
@@ -104,7 +104,7 @@ describe('ol.renderer.vector', function() {
           style.getZIndex(), 'LineString');
         const setFillStrokeStyleSpy = sinon.spy(lineStringReplay,
           'setFillStrokeStyle');
-        const drawLineStringSpy = sinon.stub(lineStringReplay, 'drawLineString').callsFake(nullFunction);
+        const drawLineStringSpy = sinon.stub(lineStringReplay, 'drawLineString').callsFake(UNDEFINED);
         renderFeature(replayGroup, feature,
           style, squaredTolerance, listener, listenerThis);
         expect(setFillStrokeStyleSpy.called).to.be(true);
@@ -119,7 +119,7 @@ describe('ol.renderer.vector', function() {
           style.getZIndex(), 'LineString');
         const setFillStrokeStyleSpy = sinon.spy(lineStringReplay,
           'setFillStrokeStyle');
-        const drawMultiLineStringSpy = sinon.stub(lineStringReplay, 'drawMultiLineString').callsFake(nullFunction);
+        const drawMultiLineStringSpy = sinon.stub(lineStringReplay, 'drawMultiLineString').callsFake(UNDEFINED);
         renderFeature(replayGroup, feature,
           style, squaredTolerance, listener, listenerThis);
         expect(setFillStrokeStyleSpy.called).to.be(true);
@@ -135,7 +135,7 @@ describe('ol.renderer.vector', function() {
           style.getZIndex(), 'Polygon');
         const setFillStrokeStyleSpy = sinon.spy(polygonReplay,
           'setFillStrokeStyle');
-        const drawPolygonSpy = sinon.stub(polygonReplay, 'drawPolygon').callsFake(nullFunction);
+        const drawPolygonSpy = sinon.stub(polygonReplay, 'drawPolygon').callsFake(UNDEFINED);
         renderFeature(replayGroup, feature,
           style, squaredTolerance, listener, listenerThis);
         expect(setFillStrokeStyleSpy.called).to.be(true);
@@ -151,7 +151,7 @@ describe('ol.renderer.vector', function() {
           style.getZIndex(), 'Polygon');
         const setFillStrokeStyleSpy = sinon.spy(polygonReplay,
           'setFillStrokeStyle');
-        const drawMultiPolygonSpy = sinon.stub(polygonReplay, 'drawMultiPolygon').callsFake(nullFunction);
+        const drawMultiPolygonSpy = sinon.stub(polygonReplay, 'drawMultiPolygon').callsFake(UNDEFINED);
         renderFeature(replayGroup, feature,
           style, squaredTolerance, listener, listenerThis);
         expect(setFillStrokeStyleSpy.called).to.be(true);
diff --git a/test/spec/ol/style/iconimagecache.test.js b/test/spec/ol/style/iconimagecache.test.js
index d53ab20e41..9128e37494 100644
--- a/test/spec/ol/style/iconimagecache.test.js
+++ b/test/spec/ol/style/iconimagecache.test.js
@@ -1,4 +1,4 @@
-import {nullFunction} from '../../../../src/ol/index.js';
+import {UNDEFINED} from '../../../../src/ol/functions.js';
 import {listen} from '../../../../src/ol/events.js';
 import {iconImageCache} from '../../../../src/ol/style.js';
 import IconImage from '../../../../src/ol/style/IconImage.js';
@@ -42,13 +42,13 @@ describe('ol.style.IconImageCache', function() {
 
       src = '0';
       iconImage = new IconImage(null, src);
-      listen(iconImage, 'change', nullFunction, false);
+      listen(iconImage, 'change', UNDEFINED, false);
       iconImageCache.set(src, null, null, iconImage);
       expect(iconImageCache.cacheSize_).to.eql(4);
 
       src = '4';
       iconImage = new IconImage(null, src);
-      listen(iconImage, 'change', nullFunction, false);
+      listen(iconImage, 'change', UNDEFINED, false);
       iconImageCache.set(src, null, null, iconImage);
       expect(iconImageCache.cacheSize_).to.eql(5);