presto-parser/src/main/java/io/prestosql/sql/tree/DefaultTraversalVisitor.java/DefaultTraversalVisitor/visitSimpleCaseExpression
class DefaultTraversalVisitor:    @Override
    protected R visitSimpleCaseExpression(SimpleCaseExpression node, C context)
    {
        process(node.getOperand(), context);
        for (WhenClause clause : node.getWhenClauses()) {
            process(clause, context);
        }

        node.getDefaultValue()
                .ifPresent(value -> process(value, context));

        return null;
    }