presto-parser/src/main/java/io/prestosql/sql/parser/AstBuilder.java/AstBuilder/visitSimpleCase
class AstBuilder:    @Override
    public Node visitSimpleCase(SqlBaseParser.SimpleCaseContext context)
    {
        return new SimpleCaseExpression(
                getLocation(context),
                (Expression) visit(context.operand),
                visit(context.whenClause(), WhenClause.class),
                visitIfPresent(context.elseExpression, Expression.class));
    }