Handle null source maps during line number selection

lib/worker/line-numbers.js

@@ -61,7 +61,7 @@ function findTest(locations, declaration) {
 const range = (start, end) => Array.from({length: end - start + 1}).fill(start).map((element, index) => element + index);
 
 const translate = (sourceMap, pos) => {
-	if (sourceMap === undefined) {
+	if (sourceMap === null) {
 		return pos;
 	}
 
@@ -88,7 +88,7 @@ export default function lineNumberSelection({file, lineNumbers = []}) {
 
 	let locations = parse(file);
 	let lookedForSourceMap = false;
-	let sourceMap;
+	let sourceMap = null;
 
 	return () => {
 		if (!lookedForSourceMap) {
@@ -98,7 +98,13 @@ export default function lineNumberSelection({file, lineNumbers = []}) {
 			// Source maps are not available before then.
 			sourceMap = findSourceMap(file);
 
-			if (sourceMap !== undefined) {
+			if (sourceMap === undefined) {
+				// Prior to Node.js 18.8.0, the value when a source map could not be found was `undefined`.
+				// This changed to `null` in <https://github.com/nodejs/node/pull/43875>.
+				sourceMap = null;
+			}
+
+			if (sourceMap !== null) {
 				locations = locations.map(({start, end}) => ({
 					start: translate(sourceMap, start),
 					end: translate(sourceMap, end),