presto-parser/src/main/java/io/prestosql/sql/parser/AstBuilder.java/AstBuilder/visitCommentTable
class AstBuilder:    @Override
    public Node visitCommentTable(SqlBaseParser.CommentTableContext context)
    {
        Optional<String> comment = Optional.empty();

        if (context.string() != null) {
            comment = Optional.of(((StringLiteral) visit(context.string())).getValue());
        }

        return new Comment(getLocation(context), Comment.Type.TABLE, getQualifiedName(context.qualifiedName()), comment);
    }