presto-parser/src/main/java/io/prestosql/sql/parser/AstBuilder.java/AstBuilder/visitDropSchema
class AstBuilder:    @Override
    public Node visitDropSchema(SqlBaseParser.DropSchemaContext context)
    {
        return new DropSchema(
                getLocation(context),
                getQualifiedName(context.qualifiedName()),
                context.EXISTS() != null,
                context.CASCADE() != null);
    }