PHP 7.3 Error: `Symphony Warning: Use of undefined constant self - assumed 'self' (this will throw an Error in a future version of PHP)

[wdebusschere]

Symphony: 2.7.8
PHP: 7.3.1

`Symphony Warning: Use of undefined constant self - assumed 'self' (this will throw an Error in a future version of PHP)
An error occurred in /Users/xxx/Sites/xxx/extensions/page_lhandles/lib/class.PLHManagerURL.php around line 144

139 // Assure we have a op_mode set
140 $op_mode = empty($op_mode) ? 'strict' : $op_mode;
141 $method = 'process'.ucfirst(strtolower($op_mode));
142
143 if (method_exists(get_class(), $method)) {
144 $path = call_user_func(array(self, $method), $old_url, $ref_handle, $target_handle);
145 }
146 else {
147 $path = trim($url, '/');
148 }`