protected Object getSingleValue() {
        Object[][] value = getValue();

        if (value == null || value.length != 1 || value[0] == null || value[0].length != 1) {
            throw new UnsupportedOperationException(
                    "Only nested object containing only one value(one column and one row) supports type conversion");
        }

        return value[0][0];
    }
Update value of the given object or create a new instance if {@code ref} is
null.

@param ref     object to update, could be null
@param columns columns
@param values  values
@return same object as {@code ref} or a new instance if it's null
clickhouse-data/src/main/java/com/clickhouse/data/value/ClickHouseNestedValue.java