Partial update of non frozen UDT field does not work.

Description

Cassandra version 3.11.4, Driver version 4.3.0, 4.20. We use mapper to generate queries.
When we make update of non frozen UDT field in entity with NullSavingStrategy.DO_NOT_SET not only not null fields of UDT are updated but all not set fields are changed to nulls.

Suppose we have database structure:

And want to update field1 and keep existing value of field2. From logs we can see that driver generates CQL:

instead of expected

That leads to full UDT overwrite instead of partial update.
It seems to be expected behavior to recursively apply NullSavingStrategy to all non immutable inner fields.

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Reporter

maxim.kislekov

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