Inserting null string into Nullable(JSON) cause error

[topofstack]

Observed

1. Define a ClickHouse table containing a Nullable(JSON) column
2. Insert a nil string into this column

Received error is:

code: 117, message: Cannot parse JSON object here:

Expected behaviour

A null value should be inserted into the table

Code example

func TestNullableJSON(t *testing.T) {
	ctx := context.Background()

	conn, err := clickhouse.Open(&clickhouse.Options{
		Addr: []string{"127.0.0.1:9000"},
		Auth: clickhouse.Auth{
			Database: "default",
			Username: "default",
		},
	})
	require.NoError(t, err, "open clickhouse")

	_ = conn.Exec(ctx, `DROP TABLE IF EXISTS t`)
	err = conn.Exec(ctx, `
		CREATE TABLE t
		(
			data Nullable(JSON)
		)
		ENGINE = Memory
	`)
	require.NoError(t, err, "create table")

	batch, err := conn.PrepareBatch(ctx, `INSERT INTO t (data) VALUES (?)`)
	require.NoError(t, err, "prepare batch")

	var s *string
	require.NoError(t, batch.Append(s))
	require.NoError(t, batch.Send(), "batch send")
}

Details

As it appears in similar issue #1638, only Batch behavior is affected.

Environment

• clickhouse-go version: v2.40.3
• Interface: ClickHouse API
• Go version: go1.24.10
• Operating system: OSX
• ClickHouse version: 25.8.5.17

[kavirajk]

@topofstack thanks for the issue. This is been fixed in this PR
#1667

And will be available in the next version.

Closing the issue. But feel free to reopen if you think that didn't fully solve the problem

[topofstack]

@kavirajk Hi, thanks for the quick response. I've downloaded the main branch and run test against it. The issue keeps reproducing.

[topofstack]

@kavirajk can you reopen the issue please?

[abhiii71]

Hi @kavirajk , thanks for reopening the issue.

I’m interested in working on this if no one is currently assigned to it.
I’m still getting familiar with the clickhouse-go codebase, but I’d like to take this as a learning contribution.
From my understanding, this looks like a batch encoder issue where nil values for Nullable(JSON) are not being handled correctly (JSON encoding seems to be attempted instead of writing the null-flag and returning early).
Please let me know if it’s okay for me to take this up, or if there’s any guidance on where you’d like the fix to go. Happy to start with a failing test if that helps.

Thanks!