TYPO3 Core

Exception:

The option $TYPO3_CONF_VARS[SYS][displayErrors] is not set to "-1", "0" or "1". in /usr/local/share/typo3/typo3_src-8.7.8/typo3/sysext/core/Classes/Core/Bootstrap.php:654

The documentation says "2" is a valid value in https://docs.typo3.org/typo3cms/CoreApiReference/8.7/ApiOverview/ErrorAndExceptionHandling/Configuration/

The code looks like

        switch ($displayErrorsSetting) {
            case -1:
                $ipMatchesDevelopmentSystem = GeneralUtility::cmpIP(GeneralUtility::getIndpEnv('REMOTE_ADDR'), $GLOBALS['TYPO3_CONF_VARS']['SYS']['devIPmask']);
                $exceptionHandlerClassName = $ipMatchesDevelopmentSystem ? $debugExceptionHandlerClassName : $productionExceptionHandlerClassName;
                $displayErrors = $ipMatchesDevelopmentSystem ? 1 : 0;
                $exceptionalErrors = $ipMatchesDevelopmentSystem ? $exceptionalErrors : 0;
                break;
            case 0:
                $exceptionHandlerClassName = $productionExceptionHandlerClassName;
                $displayErrors = 0;
                break;
            case 1:
                $exceptionHandlerClassName = $debugExceptionHandlerClassName;
                $displayErrors = 1;
                break;
            default:
                // Throw exception if an invalid option is set.
                throw new \RuntimeException(
                    'The option $TYPO3_CONF_VARS[SYS][displayErrors] is not set to "-1", "0" or "1".',
                    1476046290
                );
       }
@ini_set('display_errors', $displayErrors);

So the documentation should be adapted or the option should be realised...