Describe the bug
The Fiddle uses the same table metadata for 2 insert cases using a table with a Nullable key. When inserting with a NULL case, the value inserted on the previous block appears duplicated.

How to reproduce
Run Fiddle: https://fiddle.clickhouse.com/e957ebfd-0e54-4e96-b6db-e4c1ef06344a