Gorm default:null columns do not update with FullSaveAssociations

GORM Playground Link

https://github.com/go-gorm/playground/pull/554

Description

type User struct {
    gorm.Model
    Name      string
    Age       uint
    Birthday  *time.Time
    Account   Account
    Pets      []*Pet
    Toys      []Toy `gorm:"polymorphic:Owner"`
    CompanyID *int
    Company   Company
    ManagerID *uint
    Manager   *User
    Team      []User     `gorm:"foreignkey:ManagerID"`
    Languages []Language `gorm:"many2many:UserSpeak"`
    Friends   []*User    `gorm:"many2many:user_friends"`
    Active    bool
}

type Pet struct {
    gorm.Model
    UserID *uint
+   Name   string `gorm:"default:null"`
    Toy    Toy    `gorm:"polymorphic:Owner;"`
}

gorm code

https://github.com/go-gorm/gorm/blob/ddd3cc2502eb0a0193e10ec6360d5e83d19493a8/callbacks/create.go#L305

Because this condition is not met: (!field.HasDefaultValue || field.DefaultValueInterface != nil)

similar issues

https://github.com/go-gorm/gorm/issues/4776