Easy to reproduce:
### 20.3.13
```
SELECT 1
FORMAT JSON

{
        "meta":
        [
                {
                        "name": "1",
                        "type": "UInt8"
                }
        ],

        "data":
        [
                {
                        "1": 1
                }
        ],

        "rows": 1,

        "statistics":
        {
                "elapsed": 0.000203731,
                "rows_read": 1,
                "bytes_read": 1
        }
}
```

### 20.4.5
```
:) select 1 format JSON

SELECT 1
FORMAT JSON

{
        "meta":
        [
                {
                        "name": "1",
                        "type": "UInt8"
                }
        ],

        "data":
        [
                {
                        "1": 1
>>>>>>>> no closing bracket <<<<<<<<<<
        ],

        "rows": 1,

        "statistics":
        {
                "elapsed": 0.000771732,
                "rows_read": 1,
                "bytes_read": 1
        }
}
```
### master
```

SELECT 1
FORMAT JSON

{
        "meta":
        [
                {
                        "name": "1",
                        "type": "UInt8"
                }
        ],

        "data":
        [
                {
                        "1": 1
>>>>>>>> no closing bracket <<<<<<<<<<
        ],

        "rows": 1,

        "statistics":
        {
                "elapsed": 0.00103364,
                "rows_read": 1,
                "bytes_read": 1
        }
}

```

current_format, buf, sample, insert_format_max_block_size)
        const auto & column_defaults = columns_description.getDefaults()
        if (!column_defaults.empty())
            block_input = std::make_shared<AddingDefaultsBlockInputStream>(block_input, column_defaults, context)
        BlockInputStreamPtr async_block_input = std::make_shared<AsynchronousBlockInputStream>(block_input)
        async_block_input->readPrefix()
        hile (true)
        {
            Block block = async_block_input->read()
            /// Check if server send Log packet
            receiveLogs()
            /// Check if server send Exception packet
            checkPacket()
            if (packet_type && *packet_type == Protocol::Server::Exception)
            {
                /*
                 * We're exiting ith error, so it makes sense to kill the
                 * input stream ithout aiting for it to complete.
                 */
                async_block_input->ncel(true)
                return
            
            connection->sendDa(block)
            processed_ros += block.ros()
            if (!block)
                break
        
        async_block_input->readSuffix()
    
    /// Flush all buffers.