Updating a Nullable column value by using alter .... where ... causes to set another value!

ClickHouse version: 20.6.3.28
Engine: MergeTree
OS: Ubuntu 18.04.3 LTS

Steps to reproduce:
```sql
CREATE TABLE table1(
	id int,
	price Nullable(Int32)
)
ENGINE = MergeTree()
PARTITION BY id
ORDER BY (id);
INSERT INTO table1 (id, price) VALUES (1, 100);
ALTER TABLE table1  update price = 150 where id=1;
SELECT * FROM table1;
```
We expect the price to be `150`, but it's `93148480`:

```
┌─id─┬────price─┐
│  1 │ 93148480 │
└────┴──────────┘
```
Using `Decimal(9,2)` field instead of `Int32` would set the value  `932342.88` always. It seems there's a fixed value for each data type.

If we don't use such a `where` clause, it works correctly:
```sql
ALTER TABLE db1.table1  update price = 150 where 1=1;
┌─id─┬─price─┐
│  1 │   150 │
└────┴───────┘
```
{
        if constexpr (is_POD)
            data.resize_fill(data.size() + length, T());
        else
            data.resize(data.size() + length, T());
    }
    void popBack(size_t n) override
    {
        if constexpr (is_POD)
            data.resize_assume_reserved(data.size() - n);
        else
            data.resize(data.size() - n);
    }
    StringRef serializeValueIntoArena(size_t n, Arena & arena, char const *& begin) const override;
    const char * deserializeAndInsertFromArena(const char * pos) override;
    void updateHashWithValue(size_t n, SipHash & hash) const override;
    void updateWeakHash32(WeakHash32 & hash) const override;
    void updateHashFast(SipHash & hash) const override;
    size_t byteSize() const override
    {
        return data.size() * sizeof(data[0]);
    }
    size_t allocatedBytes() const override
    {
        if constexpr (is_POD)
            return data.allocated_bytes();
        else
            return data.capacity() * sizeof(data[0]);
    }
    void protect() override