Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Calculation/Logical.php
public static function IFERROR($testValue = '', $errorpart = '')
    {
        $testValue = ($testValue === null) ? '' : Functions::flattenSingleValue($testValue);
        $errorpart = ($errorpart === null) ? '' : Functions::flattenSingleValue($errorpart);

        return self::statementIf(Functions::isError($testValue), $errorpart, $testValue);
    }
public static function IFERROR($testValue = '', $errorpart = '')
    {
        $testValue = ($testValue === null) ? '' : Functions::flattenSingleValue($testValue);
        $errorpart = ($errorpart === null) ? '' : Functions::flattenSingleValue($errorpart);

        return self::statementIf(Functions::isError($testValue), $errorpart, $testValue);
    }
IFERROR.

Excel Function:
=IFERROR(testValue,errorpart)

@category Logical Functions

@param mixed $testValue Value to check, is also the value returned when no error
@param mixed $errorpart Value to return when testValue is an error condition

@return mixed The value of errorpart or testValue determined by error condition