public function walkCaseExpression($expression)
    {
        switch (true) {
            case ($expression instanceof AST\CoalesceExpression):
                return $this->walkCoalesceExpression($expression);

            case ($expression instanceof AST\NullIfExpression):
                return $this->walkNullIfExpression($expression);

            case ($expression instanceof AST\GeneralCaseExpression):
                return $this->walkGeneralCaseExpression($expression);

            case ($expression instanceof AST\SimpleCaseExpression):
                return $this->walkSimpleCaseExpression($expression);

            default:
                return '';
        }
    }