Null-proofing in files_watcher

doc/api/fs.md

@@ -1667,7 +1667,7 @@ added:
     should stop.
 * Returns: {AsyncIterator} of objects with the properties:
   * `eventType` {string} The type of change
-  * `filename` {string|Buffer} The name of the file changed.
+  * `filename` {string|Buffer|null} The name of the file changed.
 
 Returns an async iterator that watches for changes on `filename`, where `filename`
 is either a file or a directory.
@@ -4489,7 +4489,7 @@ changes:
   * `signal` {AbortSignal} allows closing the watcher with an AbortSignal.
 * `listener` {Function|undefined} **Default:** `undefined`
   * `eventType` {string}
-  * `filename` {string|Buffer}
+  * `filename` {string|Buffer|null}
 * Returns: {fs.FSWatcher}
 
 Watch for changes on `filename`, where `filename` is either a file or a

lib/internal/watch_mode/files_watcher.js

@@ -85,13 +85,20 @@ class FilesWatcher extends EventEmitter {
     return [...this.#watchers.keys()];
   }
 
+  [Symbol.for('emitChangeEventWithoutFilename')]() {
+    this.#watchers.values().forEach(watcher => watcher.emit('change', 'change', null));
+  }
+
   watchPath(path, recursive = true) {
     if (this.#isPathWatched(path)) {
       return;
     }
     const watcher = watch(path, { recursive });
-    watcher.on('change', (eventType, fileName) => this
-      .#onChange(recursive ? resolve(path, fileName) : path));
+    watcher.on('change', (eventType, fileName) => {
+      if (fileName != null) {
+        this.#onChange(recursive ? resolve(path, fileName) : path);
+      }
+    });
     this.#watchers.set(path, { handle: watcher, recursive });
     if (recursive) {
       this.#removeWatchedChildren(path);

test/parallel/test-watch-mode-files_watcher.mjs

@@ -159,4 +159,12 @@ describe('watch mode file watcher', () => {
     }
     assert.deepStrictEqual(watcher.watchedPaths, expected);
   });
+
+  it('should ignore watch event without filename', async () => {
+    watcher.on('changed', common.mustNotCall());
+    watcher.watchPath(tmpdir.path);
+    watcher[Symbol.for('emitChangeEventWithoutFilename')]();
+    // Wait for this long to make sure changes are not triggered
+    await setTimeout(1000);
+  });  
 });