After installing Moodle, ensure that "Enable accessibility tools" is turned on (checked) in the "Site administration / Advanced features" section. In the "Site administration / Plugins / Admin tools / Accessibility / Brickfield registration", ensure that you have registered your site. In the "Site administration / Plugins / Admin tools / Accessibility / Accessibility toolkit settings", ensure that you have "Enable analysis requests" enabled (checked). In a test course section description, add the following raw HTML content: <span style="color: -10234; background-color: 1050743;">This is content.</span> Save the content. In the same course, access the "Accessibility toolkit" selection from the course actions menu. If the course has not been submitted for analysis, press the "Submit for analysis" button. Run the "Process content analysis requests" scheduled task, either manually from the "Site administration / Server / Tasks / Scheduled tasks" page (preferred) or from the cron. Check there is no error while running the task (without the patch, the error "Argument 2 passed to tool_brickfield\local\htmlchecker\common\brickfield_accessibility_color_test::luminosity() must be of the type string, null given" is displayed).