Fatal error: Unsupported operand types

After updating view module to 6x-2.18, my current opportunity view throwing fatal error.

Fatal error: Unsupported operand types in /home/raqorgau/public_html/sites/all/modules/views/handlers/views_handler_field.inc on line 493

The code in question is:

$alter = $item + $this->options['alter'];

which works after replacing + with .

$alter = $item . $this->options['alter'];

This appears to fix the problem for me, though my PHP knowledge isn't strong enough to know whether this will break other parts of Views. Can anyone shed light on this?

Thanks