Join or Leave button is now working in user dashboard

• Type: Bug
• Status: Closed
• Resolution: No Longer Reproducible
• Affects Version/s: 7.3.X
• Fix Version/s: None
• Component/s: Site Memberships
• Labels:
  • 7.3-blocker
  • QA-AUTOMATION
  • QA-FP
• Fix Priority: 4
• Bug Type: Regression Bug
• QA Test Name:
  • LocalFile.MySites#JoinSiteOpen
  • LocalFile.MySites#LeaveSite
• QA Test Score: 9

Steps to Reproduce:

1. Create a site named "Test Site".
2. Create a user and log in.
3. In user's dashboard -> Available Sites, try to join "Test Site".

Expected result:
User can join the new site.

Actual result:
After clicking join, nothing happened.

Note: This issue also happens on Leave button if a user is leaving a site via dashboard. Error in browser console:

TypeError: Class constructor DefaultEventHandler cannot be invoked without 'new'
    at new SiteDropdownDefaultEventHandler (SiteDropdownDefaultEventHandler.es.js?languageId=en_US:77:98)
    at <anonymous>:36:302
    at <anonymous>:37:69
    at loader.js:463:12
    at loader.js:427:12