As a simple background, I have a table `foo`, with a nullable int foreign key `bar_id`. I have a function that removes the `bar` association from `foo`, aka set it to `NULL`.

I have tried everything: I tried using `sql.NullInt64` as the column type, and then 

```
foo.BarId.Valid = false // even set Int64 = 0 for good measure
db.Save(&foo) // with LogMode(true)

```

`bar_id` was not updated in the UPDATE statement

I tried:

```
db.Raw("UPDATE foo SET bar_id = NULL WHERE id = ?", foo.ID).Row().Scan(&foo)

```

The SQL was correct thankfully, but the object is not updated. I don't think my version of gorm has `Error` either.

I tried changing the type of Foo.BarId to an `*int64`, and setting the pointer to `nil`, but the output query didn't change `bar_id` to NULL.

What do I need to do?