[client-v2] failing when serializing nested nullable columns.

[javiercj93]

Describe the bug

Create the following table

Steps to reproduce

1. Create a table with a nested column which has a nullable field.

   CREATE TABLE test.visits
   (
   CounterID UInt32,
   StartDate Date,
   Sign Int8,
   IsNew UInt8,
   VisitID UInt64,
   UserID UInt64,
   Goals Nested
   (
       ID UInt32,
       Serial UInt32,
       EventTime DateTime,
       Price Nullable(Int32),
       OrderID String,
       CurrencyID UInt32
   )
   ) ENGINE = CollapsingMergeTree(StartDate, intHash32(UserID), (CounterID, StartDate, intHash32(UserID), VisitID), 8192, Sign)

2. Insert a visit with goals Price containing a null value:

Expected behaviour

Since it is possible to create such nullable fields, the client should be able to handle them and serialize them successfully.

Error log

Caused by: java.lang.IllegalArgumentException: Cannot convert null to Integer
        at com.clickhouse.client.api.internal.SerializerUtils.convertToInteger(SerializerUtils.java:225)

Environment

• Client version: 0.7.0
• Language version: java17
• OS:

ClickHouse server

• ClickHouse Server version: 23.3.18.15

I have created this PR which fixes the issue (apparently)

[chernser]

@javiercj93 Thank you for reporting! We will review the PR.