Wordpress - Civicrm 5.16 upgrade to 5.30 issue - Notice: Undefined index query in /wp-content/plugins/civicrm/civicrm.php on line 483

Question

When upgrading our site from Civi 5.16 to the latest 5.30, when I point my browser to run the upgrade at: http://example.org/wp-admin/admin.php?page=CiviCRM&q=civicrm/upgrade&reset=1

I get the to the update page, which has the following:

The database will be upgraded from 5.16.0 to 5.30.0.

Then long list of warnings about default copies of message templates etc. At the end of this, when I click on the "Upgrade Now" button, I get this message and nothing else happens:

Notice: Undefined index query in .../wp-content/plugins/civicrm/civicrm.php on line 483

I'm running Wordpress 4.9. No our site is down and I need help to resolve this upgrade issue.

Answer 1

Comment out line 391 of that file - so that it reads like this:

// add_filter( 'heartbeat_settings', array( $this, 'heartbeat' ), 1000, 1 );

Then try the upgrade again.