presto-jdbc/src/main/java/io/prestosql/jdbc/PrestoResultSetMetaData.java/PrestoResultSetMetaData/isNullable
class PrestoResultSetMetaData:    @Override
    public int isNullable(int column)
            throws SQLException
    {
        ColumnInfo.Nullable nullable = column(column).getNullable();
        switch (nullable) {
            case NO_NULLS:
                return columnNoNulls;
            case NULLABLE:
                return columnNullable;
            case UNKNOWN:
                return columnNullableUnknown;
        }
        throw new SQLException("Unhandled nullable type: " + nullable);
    }