AG-48914 Fix error on null event type in prevent-addEventListener

Squashed commit of the following:

commit ebfbfd3
Author: Anatolii Khmarskii <a.khmarskii@adguard.com>
Date:   Fri Dec 19 17:58:09 2025 +0300

    AG-48914 Fix error on null event type in prevent-addEventListener

Author: techi9

CHANGELOG.md

@@ -17,6 +17,12 @@ The format is based on [Keep a Changelog], and this project adheres to [Semantic
 - Support for React elements that don't respond to native clicks
   in `trusted-click-element` scriptlet [#542].
 
+### Fixed
+
+- Do not throw error on `null` event type in `prevent-addEventListener` scriptlet [#539].
+
+[#539]: https://github.com/AdguardTeam/Scriptlets/issues/539
+
 [#542]: https://github.com/AdguardTeam/Scriptlets/issues/542
 
 ## [v2.2.14] - 2025-12-16

src/helpers/add-event-listener-utils.ts

@@ -6,7 +6,9 @@
  */
 export const validateType = (type: unknown): boolean => {
     // https://github.com/AdguardTeam/Scriptlets/issues/125
-    return typeof type !== 'undefined';
+    return typeof type !== 'undefined'
+        // https://github.com/AdguardTeam/Scriptlets/issues/539
+        && type !== null;
 };
 
 /**

tests/scriptlets/prevent-addEventListener.test.js

@@ -82,6 +82,27 @@ test('should not prevent addEventListener if event is undefined', (assert) => {
     clearGlobalProps(testProp);
 });
 
+test('should not throw error when event type is null', (assert) => {
+    const TEST_EVENT_NAME = 'testEvent';
+    runScriptlet(name, [TEST_EVENT_NAME]);
+
+    const testProp = 'test';
+    window[testProp] = 'start';
+
+    // This should not throw an error
+    assert.expect(2);
+    try {
+        document.addEventListener(null, () => {});
+        window[testProp] = 'end';
+    } catch (e) {
+        assert.ok(false, `Should not throw error: ${e.message}`);
+    }
+
+    assert.strictEqual(window[testProp], 'end', 'property should be changed to end');
+    assert.strictEqual(window.hit, undefined, 'hit should not be fired');
+    clearGlobalProps(testProp);
+});
+
 test('does not allow to add event listener', (assert) => {
     const scriptletArgs = ['click', 'clicked'];
     runScriptlet(name, scriptletArgs);