From 25d9fa1efe2d09b4267eda231638d349f85f9ec2 Mon Sep 17 00:00:00 2001
From: Andreas Hocevar <andreas.hocevar@gmail.com>
Date: Thu, 26 Sep 2019 14:58:18 +0200
Subject: [PATCH 1/2] Require type and listener for
 addEventListener/removeEventListener

---
 src/ol/events/Target.js | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/ol/events/Target.js b/src/ol/events/Target.js
index fa5269b116..773dd53537 100644
--- a/src/ol/events/Target.js
+++ b/src/ol/events/Target.js
@@ -57,6 +57,9 @@ class Target extends Disposable {
    * @param {import("../events.js").ListenerFunction} listener Listener.
    */
   addEventListener(type, listener) {
+    if (!type || !listener) {
+      return;
+    }
     let listeners = this.listeners_[type];
     if (!listeners) {
       listeners = this.listeners_[type] = [];
@@ -146,6 +149,9 @@ class Target extends Disposable {
    * @param {import("../events.js").ListenerFunction} listener Listener.
    */
   removeEventListener(type, listener) {
+    if (!type || !listener) {
+      return;
+    }
     const listeners = this.listeners_[type];
     if (listeners) {
       const index = listeners.indexOf(listener);

From d2e33a0df0b38f1eb78382ea628140d0891da33f Mon Sep 17 00:00:00 2001
From: Andreas Hocevar <andreas.hocevar@gmail.com>
Date: Thu, 26 Sep 2019 15:20:29 +0200
Subject: [PATCH 2/2] Add a test that shows the fixed issue

---
 test/spec/ol/events/eventtarget.test.js | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/test/spec/ol/events/eventtarget.test.js b/test/spec/ol/events/eventtarget.test.js
index 4cc6c73aff..9aa3a9641b 100644
--- a/test/spec/ol/events/eventtarget.test.js
+++ b/test/spec/ol/events/eventtarget.test.js
@@ -64,6 +64,11 @@ describe('ol.events.EventTarget', function() {
       eventTarget.removeEventListener('foo', spy1, false);
       expect(eventTarget.listeners_['foo']).to.have.length(1);
     });
+    it.only('does nothing when called with undefined listener', function() {
+      eventTarget.addEventListener('foo', spy1);
+      eventTarget.removeEventListener('foo', undefined);
+      expect(eventTarget.listeners_['foo']).to.eql([spy1]);
+    });
   });
 
   describe('#dispatchEvent()', function() {