UserAgent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.80 Safari/537.36

Steps to reproduce the problem:
1. Have an ASP control with an onClick event, e.g. <asp:Label ID="ThisLabel" runat="server" onclick="Label_Click(event)" />
2. Click the label while the code is running
3. In the onClick function, the 'event' parameter is null

function Label_Click(event){
  // prevent any other click handlers firing
  event.stopPropagation(); 

  // do other stuff after this
}

What is the expected behavior?
The 'event' parameter should not be null. The code still works in IE, Firefox, Edge, and version 70 of Chrome

What went wrong?
The 'event' parameter is null, and thus the function triggered a NullReferenceException

Did this work before? Yes 70

Chrome version: 71.0.3578.80  Channel: stable
OS Version: 10.0
Flash Version: