diff --git a/src/ol/MapBrowserEventHandler.js b/src/ol/MapBrowserEventHandler.js
index f35ad17811..b17513cd53 100644
--- a/src/ol/MapBrowserEventHandler.js
+++ b/src/ol/MapBrowserEventHandler.js
@@ -59,7 +59,7 @@ class MapBrowserEventHandler extends Target {
     /**
      * The most recent "down" type event (or null if none have occurred).
      * Set on pointerdown.
-     * @type {PointerEvent}
+     * @type {PointerEvent|null}
      * @private
      */
     this.down_ = null;
diff --git a/src/ol/css.js b/src/ol/css.js
index 89d000e1de..0e5b6e709d 100644
--- a/src/ol/css.js
+++ b/src/ol/css.js
@@ -91,7 +91,7 @@ const fontRegExMatchIndex = [
  * Get the list of font families from a font spec.  Note that this doesn't work
  * for font families that have commas in them.
  * @param {string} fontSpec The CSS font property.
- * @return {FontParameters} The font parameters (or null if the input spec is invalid).
+ * @return {FontParameters|null} The font parameters (or null if the input spec is invalid).
  */
 export const getFontParameters = function (fontSpec) {
   const match = fontSpec.match(fontRegEx);
diff --git a/src/ol/format/KML.js b/src/ol/format/KML.js
index 4c87601b00..076f45b34a 100644
--- a/src/ol/format/KML.js
+++ b/src/ol/format/KML.js
@@ -195,13 +195,13 @@ const KML_SERIALIZERS = makeStructureNS(NAMESPACE_URIS, {
 let DEFAULT_COLOR;
 
 /**
- * @type {Fill}
+ * @type {Fill|null}
  */
 let DEFAULT_FILL_STYLE = null;
 
 /**
  * Get the default fill style (or null if not yet set).
- * @return {Fill} The default fill style.
+ * @return {Fill|null} The default fill style.
  */
 export function getDefaultFillStyle() {
   return DEFAULT_FILL_STYLE;
@@ -233,13 +233,13 @@ let DEFAULT_IMAGE_STYLE_SIZE;
 let DEFAULT_IMAGE_STYLE_SRC;
 
 /**
- * @type {import("../style/Image.js").default}
+ * @type {import("../style/Image.js").default|null}
  */
 let DEFAULT_IMAGE_STYLE = null;
 
 /**
  * Get the default image style (or null if not yet set).
- * @return {import("../style/Image.js").default} The default image style.
+ * @return {import("../style/Image.js").default|null} The default image style.
  */
 export function getDefaultImageStyle() {
   return DEFAULT_IMAGE_STYLE;
@@ -251,13 +251,13 @@ export function getDefaultImageStyle() {
 let DEFAULT_NO_IMAGE_STYLE;
 
 /**
- * @type {Stroke}
+ * @type {Stroke|null}
  */
 let DEFAULT_STROKE_STYLE = null;
 
 /**
  * Get the default stroke style (or null if not yet set).
- * @return {Stroke} The default stroke style.
+ * @return {Stroke|null} The default stroke style.
  */
 export function getDefaultStrokeStyle() {
   return DEFAULT_STROKE_STYLE;
@@ -269,39 +269,39 @@ export function getDefaultStrokeStyle() {
 let DEFAULT_TEXT_STROKE_STYLE;
 
 /**
- * @type {Text}
+ * @type {Text|null}
  */
 let DEFAULT_TEXT_STYLE = null;
 
 /**
  * Get the default text style (or null if not yet set).
- * @return {Text} The default text style.
+ * @return {Text|null} The default text style.
  */
 export function getDefaultTextStyle() {
   return DEFAULT_TEXT_STYLE;
 }
 
 /**
- * @type {Style}
+ * @type {Style|null}
  */
 let DEFAULT_STYLE = null;
 
 /**
  * Get the default style (or null if not yet set).
- * @return {Style} The default style.
+ * @return {Style|null} The default style.
  */
 export function getDefaultStyle() {
   return DEFAULT_STYLE;
 }
 
 /**
- * @type {Array<Style>}
+ * @type {Array<Style>|null}
  */
 let DEFAULT_STYLE_ARRAY = null;
 
 /**
  * Get the default style array (or null if not yet set).
- * @return {Array<Style>} The default style.
+ * @return {Array<Style>|null} The default style.
  */
 export function getDefaultStyleArray() {
   return DEFAULT_STYLE_ARRAY;
diff --git a/src/ol/format/WKB.js b/src/ol/format/WKB.js
index fa537ffbe3..0c65d11092 100644
--- a/src/ol/format/WKB.js
+++ b/src/ol/format/WKB.js
@@ -62,7 +62,7 @@ class WkbReader {
     this.isLittleEndian_ = false;
     this.hasZ_ = false;
     this.hasM_ = false;
-    /** @type {number} */
+    /** @type {number|null} */
     this.srid_ = null;
 
     this.layout_ = GeometryLayout.XY;
@@ -356,7 +356,7 @@ class WkbReader {
   }
 
   /**
-   * @return {number} SRID in the EWKB. `null` if not defined.
+   * @return {number|null} SRID in the EWKB. `null` if not defined.
    */
   getSrid() {
     return this.srid_;
diff --git a/src/ol/geom/LineString.js b/src/ol/geom/LineString.js
index 1cedd06d0a..8d624ea437 100644
--- a/src/ol/geom/LineString.js
+++ b/src/ol/geom/LineString.js
@@ -166,7 +166,7 @@ class LineString extends SimpleGeometry {
    *
    * @param {number} m M.
    * @param {boolean} [opt_extrapolate] Extrapolate. Default is `false`.
-   * @return {import("../coordinate.js").Coordinate} Coordinate.
+   * @return {import("../coordinate.js").Coordinate|null} Coordinate.
    * @api
    */
   getCoordinateAtM(m, opt_extrapolate) {
diff --git a/src/ol/geom/MultiLineString.js b/src/ol/geom/MultiLineString.js
index 25d547ebee..5314f20e26 100644
--- a/src/ol/geom/MultiLineString.js
+++ b/src/ol/geom/MultiLineString.js
@@ -169,7 +169,7 @@ class MultiLineString extends SimpleGeometry {
    * @param {number} m M.
    * @param {boolean} [opt_extrapolate] Extrapolate. Default is `false`.
    * @param {boolean} [opt_interpolate] Interpolate. Default is `false`.
-   * @return {import("../coordinate.js").Coordinate} Coordinate.
+   * @return {import("../coordinate.js").Coordinate|null} Coordinate.
    * @api
    */
   getCoordinateAtM(m, opt_extrapolate, opt_interpolate) {
diff --git a/src/ol/geom/Polygon.js b/src/ol/geom/Polygon.js
index af17e62eb3..256dd1cea1 100644
--- a/src/ol/geom/Polygon.js
+++ b/src/ol/geom/Polygon.js
@@ -275,7 +275,7 @@ class Polygon extends SimpleGeometry {
    * at index `1` and beyond.
    *
    * @param {number} index Index.
-   * @return {LinearRing} Linear ring.
+   * @return {LinearRing|null} Linear ring.
    * @api
    */
   getLinearRing(index) {
diff --git a/src/ol/geom/flat/interpolate.js b/src/ol/geom/flat/interpolate.js
index d87709ca5e..1d3302709d 100644
--- a/src/ol/geom/flat/interpolate.js
+++ b/src/ol/geom/flat/interpolate.js
@@ -74,7 +74,7 @@ export function interpolatePoint(
  * @param {number} stride Stride.
  * @param {number} m M.
  * @param {boolean} extrapolate Extrapolate.
- * @return {import("../../coordinate.js").Coordinate} Coordinate.
+ * @return {import("../../coordinate.js").Coordinate|null} Coordinate.
  */
 export function lineStringCoordinateAtM(
   flatCoordinates,
@@ -147,7 +147,7 @@ export function lineStringCoordinateAtM(
  * @param {number} m M.
  * @param {boolean} extrapolate Extrapolate.
  * @param {boolean} interpolate Interpolate.
- * @return {import("../../coordinate.js").Coordinate} Coordinate.
+ * @return {import("../../coordinate.js").Coordinate|null} Coordinate.
  */
 export function lineStringsCoordinateAtM(
   flatCoordinates,
diff --git a/src/ol/geom/flat/textpath.js b/src/ol/geom/flat/textpath.js
index d4ca0e7ed9..18eff716a4 100644
--- a/src/ol/geom/flat/textpath.js
+++ b/src/ol/geom/flat/textpath.js
@@ -17,7 +17,7 @@ import {rotate} from './transform.js';
  * @param {string} font The font.
  * @param {Object<string, number>} cache A cache of measured widths.
  * @param {number} rotation Rotation to apply to the flatCoordinates to determine whether text needs to be reversed.
- * @return {Array<Array<*>>} The result array (or null if `maxAngle` was
+ * @return {Array<Array<*>>|null} The result array (or null if `maxAngle` was
  * exceeded). Entries of the array are x, y, anchorX, angle, chunk.
  */
 export function drawTextOnPath(
diff --git a/src/ol/interaction/Interaction.js b/src/ol/interaction/Interaction.js
index 1e59919055..4614e718e3 100644
--- a/src/ol/interaction/Interaction.js
+++ b/src/ol/interaction/Interaction.js
@@ -66,7 +66,7 @@ class Interaction extends BaseObject {
 
     /**
      * @private
-     * @type {import("../PluggableMap.js").default}
+     * @type {import("../PluggableMap.js").default|null}
      */
     this.map_ = null;
 
@@ -85,7 +85,7 @@ class Interaction extends BaseObject {
 
   /**
    * Get the map associated with this interaction.
-   * @return {import("../PluggableMap.js").default} Map.
+   * @return {import("../PluggableMap.js").default|null} Map.
    * @api
    */
   getMap() {
@@ -116,7 +116,7 @@ class Interaction extends BaseObject {
    * Remove the interaction from its current map and attach it to the new map.
    * Subclasses may set up event handlers to get notified about changes to
    * the map here.
-   * @param {import("../PluggableMap.js").default} map Map.
+   * @param {import("../PluggableMap.js").default|null} map Map.
    */
   setMap(map) {
     this.map_ = map;
diff --git a/src/ol/interaction/Select.js b/src/ol/interaction/Select.js
index 8436cd1ff5..1e72a18c77 100644
--- a/src/ol/interaction/Select.js
+++ b/src/ol/interaction/Select.js
@@ -334,7 +334,7 @@ class Select extends Interaction {
   /**
    * Remove the interaction from its current map, if any,  and attach it to a new
    * map, if any. Pass `null` to just remove the interaction from the current map.
-   * @param {import("../PluggableMap.js").default} map Map.
+   * @param {import("../PluggableMap.js").default|null} map Map.
    * @api
    */
   setMap(map) {
diff --git a/src/ol/layer/Layer.js b/src/ol/layer/Layer.js
index 0c55fdc460..0ea58b080f 100644
--- a/src/ol/layer/Layer.js
+++ b/src/ol/layer/Layer.js
@@ -188,7 +188,7 @@ class Layer extends BaseLayer {
 
   /**
    * Get the layer source.
-   * @return {SourceType} The layer source (or `null` if not yet set).
+   * @return {SourceType|null} The layer source (or `null` if not yet set).
    * @observable
    * @api
    */
@@ -197,7 +197,7 @@ class Layer extends BaseLayer {
   }
 
   /**
-   * @return {SourceType} The source being rendered.
+   * @return {SourceType|null} The source being rendered.
    */
   getRenderSource() {
     return this.getSource();
@@ -333,7 +333,7 @@ class Layer extends BaseLayer {
 
   /**
    * Set the layer source.
-   * @param {SourceType} source The layer source.
+   * @param {SourceType|null} source The layer source.
    * @observable
    * @api
    */
diff --git a/src/ol/proj.js b/src/ol/proj.js
index 883f464783..7a5795c21c 100644
--- a/src/ol/proj.js
+++ b/src/ol/proj.js
@@ -158,7 +158,7 @@ export function addProjections(projections) {
  * @param {ProjectionLike} projectionLike Either a code string which is
  *     a combination of authority and identifier such as "EPSG:4326", or an
  *     existing projection object, or undefined.
- * @return {Projection} Projection object, or null if not in list.
+ * @return {Projection|null} Projection object, or null if not in list.
  * @api
  */
 export function get(projectionLike) {
@@ -533,7 +533,7 @@ export function transformWithProjections(
 }
 
 /**
- * @type {?Projection}
+ * @type {Projection|null}
  */
 let userProjection = null;
 
@@ -560,7 +560,7 @@ export function clearUserProjection() {
  * Get the projection for coordinates supplied from and returned by API methods.
  * Note that this method is not yet a part of the stable API.  Support for user
  * projections is not yet complete and should be considered experimental.
- * @return {?Projection} The user projection (or null if not set).
+ * @return {Projection|null} The user projection (or null if not set).
  */
 export function getUserProjection() {
   return userProjection;
diff --git a/src/ol/source/Source.js b/src/ol/source/Source.js
index 1642417d74..a2e833fbc9 100644
--- a/src/ol/source/Source.js
+++ b/src/ol/source/Source.js
@@ -219,7 +219,7 @@ class Source extends BaseObject {
 /**
  * Turns the attributions option into an attributions function.
  * @param {AttributionLike|undefined} attributionLike The attribution option.
- * @return {?Attribution} An attribution function (or null).
+ * @return {Attribution|null} An attribution function (or null).
  */
 function adaptAttributions(attributionLike) {
   if (!attributionLike) {
diff --git a/src/ol/source/Vector.js b/src/ol/source/Vector.js
index 77f4f61bd8..b3c540559a 100644
--- a/src/ol/source/Vector.js
+++ b/src/ol/source/Vector.js
@@ -293,7 +293,7 @@ class VectorSource extends Source {
 
     /**
      * @private
-     * @type {Collection<import("../Feature.js").default<Geometry>>}
+     * @type {Collection<import("../Feature.js").default<Geometry>>|null}
      */
     this.featuresCollection_ = null;
 
@@ -683,7 +683,7 @@ class VectorSource extends Source {
    * Get the features collection associated with this source. Will be `null`
    * unless the source was configured with `useSpatialIndex` set to `false`, or
    * with an {@link module:ol/Collection} as `features`.
-   * @return {Collection<import("../Feature.js").default<Geometry>>} The collection of features.
+   * @return {Collection<import("../Feature.js").default<Geometry>>|null} The collection of features.
    * @api
    */
   getFeaturesCollection() {
diff --git a/src/ol/source/WMTS.js b/src/ol/source/WMTS.js
index b176cd4ed1..b17f79de51 100644
--- a/src/ol/source/WMTS.js
+++ b/src/ol/source/WMTS.js
@@ -367,7 +367,7 @@ export default WMTS;
  *  - format - {string} Image format for the layer. Default is the first
  *       format returned in the GetCapabilities response.
  *  - crossOrigin - {string|null|undefined} Cross origin. Default is `undefined`.
- * @return {?Options} WMTS source options object or `null` if the layer was not found.
+ * @return {Options|null} WMTS source options object or `null` if the layer was not found.
  * @api
  */
 export function optionsFromCapabilities(wmtsCap, config) {
diff --git a/src/ol/webgl/Helper.js b/src/ol/webgl/Helper.js
index f7ceb515b8..c8fb64819e 100644
--- a/src/ol/webgl/Helper.js
+++ b/src/ol/webgl/Helper.js
@@ -469,7 +469,7 @@ class WebGLHelper extends Disposable {
    * Get a WebGL extension.  If the extension is not supported, null is returned.
    * Extensions are cached after they are enabled for the first time.
    * @param {string} name The extension name.
-   * @return {Object} The extension or null if not supported.
+   * @return {Object|null} The extension or null if not supported.
    */
   getExtension(name) {
     if (name in this.extensionCache_) {