Uncaught TypeError: Invalid value used in weak set

ボタンがクリックされたらaddEventListenerで You are buying it!と表示させたいです。実際にボタンをクリックするとYou are buying it!と表示されますが、同時に以下のようなエラーも発生します。原因がわかりませんので、ご教授願います。

Uncaught TypeError: Invalid value used in weak set
 at WeakSet.add (<anonymous>)
 at content.js:8851
 at Array.forEach (<anonymous>)
 at content.js:8850
 at Array.forEach (<anonymous>)
 at IframeVisibilityNotifier.onMutation (content.js:8844)
 at PAMMutionObserver.EventEmitter.emit (content.js:1953)
 at PAMMutionObserver.onMutation (content.js:6357)

・indexjs

<!DOCTYPE html>
<html lang="ja">

<head>
  <meta charset="utf-8">
  <title>JavaScript Basics</title>
</head>

<body>
  <h2>Buy buttons</h2>

  <button class="buy">Buy Item 1</button>
  <button class="buy">Buy Item 2</button>
  <button class="buy">Buy Item 3</button>
  <button class="buy">Buy Item 4</button>
  <button class="buy">Buy Item 5</button>
  <button class="buy">Buy Item 6</button>
  <button class="buy">Buy Item 7</button>
  <button class="buy">Buy Item 8</button>
  <button class="buy">Buy Item 9</button>
  <button class="buy">Buy Item 10</button>

  <script src="./JS/event.js"></script>
</body>

</html>

・event.js

  const buyButtons = document.querySelectorAll('button.buy');
  
  function handleBuyButtonClick(){
    console.log('You are buying it!')
  }
  buyButtons.forEach(function(buyButton){
    buyButton.addEventListener('click', handleBuyButtonClick);
  });