Move the nullFunction to ol/functions

And rename it to `UNDEFINED`.

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;
 
 
 /**

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;
 
 
 /**

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);

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(