Error writing empty LowCardinality(String) array in 3.1.2

[Mayrond]

Hi! After updating from version 3.1.1 to 3.1.2, I encountered an error in saving empty string arrays with LowCardinality.

.net target: 8.0 Docker: clickhouse/clickhouse-server:23.8-alpine

I have 2 examples with different errors, first one:

using Octonica.ClickHouseClient;

const string connectionString = "Host=localhost;Port=9000;User=default;Password=;";

var connection = new ClickHouseConnection(connectionString);
connection.Open();

var dropTableCommand = connection.CreateCommand("DROP TABLE IF EXISTS test_table");
dropTableCommand.ExecuteNonQuery();

var createTableCommand = connection.CreateCommand(
    $"""
     CREATE TABLE test_table
     (
        id Int32,
        strings Array(LowCardinality(String))
     ) ENGINE = MergeTree()
     ORDER BY id;
     """);

createTableCommand.ExecuteNonQuery();

var columns = new Dictionary<string, object?>
{
    { "id", new[] { 123 } },
    { "strings", new[] { Array.Empty<string>() } }
};

await using var writer = await connection.CreateColumnWriterAsync(
    $"insert into test_table(id, strings) values",
    CancellationToken.None);

await writer.WriteTableAsync(columns, 1, CancellationToken.None);

I'm getting the error: Octonica.ClickHouseClient.Exceptions.ClickHouseServerException: DB::Exception: Empty query If I remove LowCardinality, it works fine.

Similar example:

using Octonica.ClickHouseClient;

const string connectionString = "Host=localhost;Port=9000;User=default;Password=;";

var connection = new ClickHouseConnection(connectionString);
connection.Open();

var dropTableCommand = connection.CreateCommand("DROP TABLE IF EXISTS test_table");
dropTableCommand.ExecuteNonQuery();

var createTableCommand = connection.CreateCommand(
    $"""
     CREATE TABLE test_table
     (
        id Int32,
        strings Array(LowCardinality(String)),
        any_field Int32,
     ) ENGINE = MergeTree()
     ORDER BY id;
     """);

createTableCommand.ExecuteNonQuery();

var columns = new Dictionary<string, object?>
{
    { "id", new[] { 123 } },
    { "strings", new[] { Array.Empty<string>() } },
    { "any_field", new[] { 321 } }
};

await using var writer = await connection.CreateColumnWriterAsync(
    $"insert into test_table(id, strings, any_field) values",
    CancellationToken.None);

await writer.WriteTableAsync(columns, 1, CancellationToken.None);

Error: Octonica.ClickHouseClient.Exceptions.ClickHouseServerException DB::Exception: Syntax error (data type): failed at position 1 (''): . Unrecognized token: ''

Also works fine without LowCardinality.

[victor-sushko]

The bug was fixed in the version 3.1.3.