Fix fatal error "Class modRequest not found" in MODX 2.x

[halftrainedharry]

In MODX 2.x, when rendering an element on the front-end (assets/components/fred/web/endpoints/ajax.php?modx=2&action=render-element) a fatal error occurs:

Fatal error: Uncaught Error: Class 'modRequest' not found in .../core/components/fred/src/Traits/Endpoint/Ajax/RenderElement.php:119
Stack trace:
#0 .../core/components/fred/src/Traits/Endpoint/Ajax/Endpoint.php(40): Fred/v2/Endpoint/Ajax/RenderElement->process()
#1 .../core/components/fred/src/v2/Endpoint/Ajax.php(64): Fred/v2/Endpoint/Ajax/Endpoint->run()
#2 .../assets/components/fred/web/endpoints/ajax.php(22): Fred/v2/Endpoint/Ajax->run()

Related forum topic: https://community.modx.com/t/problem-upgrading-fred-to-version-3-0-in-modx-2-8-7/7915/13

Fred 3.0.0-pl
MODX 2.8.7-pl