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 │
└────┴───────┘
```
{
        return column->convertToFullColumnIfConst();
    }
    static ColumnPtr makeNullableColumnIfNot(const ColumnPtr & column)
    {
        auto materialized = materializeColumnIfConst(column);
        if (isColumnNullable(*materialized))
            return materialized;
        return ColumnNullable::create(materialized, ColumnUInt8::create(column->size(), 0));
    }
    static ColumnPtr getNestedColumn(const ColumnPtr & column)
    {
        if (const auto * nullable = checkAndGetColumn<ColumnNullable>(*column))
            return nullable->getNestedColumnPtr();
        return column;
    }
    bool executeForNullableThenElse(Block & block, const ColumnNumbers & arguments, size_t result, size_t input_rows_count) const
    {
        const ColumnWithTypeAndName & arg_cond = block.getByPosition(arguments[0]);
        const ColumnWithTypeAndName & arg_then = block.getByPosition(arguments[1]);
        const ColumnWithTypeAndName & arg_else = block.getByPosition(arguments[2]);
        const auto * then_is_nullable = checkAndGetColumn<ColumnNullable>(*arg_then.column);
        const auto * else_is_nullable = checkAndGetColumn<ColumnNullable>(*arg_else.column);
        if (!then_is_nullable && !else_is_nullable)