@Override
    public int isNullable(int param) throws SQLException {
        checkParamIndex(param);
        return ParameterMetaData.parameterNullableUnknown;
    }
Always returns {@code ParameterMetaData.parameterNullableUnknown}.

@param param parameter index starting from 1
@return ParameterMetaData.parameterNullableUnknown
jdbc-v2/src/main/java/com/clickhouse/jdbc/metadata/ParameterMetaDataImpl.java