presto-base-jdbc/src/main/java/io/prestosql/plugin/jdbc/JdbcRecordCursor.java/JdbcRecordCursor/isNull
class JdbcRecordCursor:    @Override
    public boolean isNull(int field)
    {
        checkState(!closed, "cursor is closed");
        checkArgument(field < columnHandles.length, "Invalid field index");

        try {
            // JDBC is kind of dumb: we need to read the field and then ask
            // if it was null, which means we are wasting effort here.
            // We could save the result of the field access if it matters.
            resultSet.getObject(field + 1);

            return resultSet.wasNull();
        }
        catch (SQLException | RuntimeException e) {
            throw handleSqlException(e);
        }
    }