Improve some null types for strictNullChecks

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,

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(