OtherID string
		Data    string
	}

	DB.Migrator().DropTable(&Thing{})
	DB.Migrator().CreateTable(&Thing{})
	if err := DB.Exec("ALTER TABLE things ADD CONSTRAINT some_id_other_id_unique UNIQUE (some_id, other_id)").Error; err != nil {
		t.Error(err)
	}

	thing := Thing{
		SomeID:  "1234",
		OtherID: "1234",
		Data:    "something",
	}

	DB.Create(&thing)

	thing2 := Thing{

		OtherID string
		Data    string
	}

	DB.Migrator().DropTable(&Thing{})
	DB.Migrator().CreateTable(&Thing{})
	if err := DB.Exec("ALTER TABLE things ADD CONSTRAINT some_id_other_id_unique UNIQUE (some_id, other_id)").Error; err != nil {
		t.Error(err)
	}

	thing := Thing{
		SomeID:  "1234",
		OtherID: "1234",
		Data:    "something",
	}

	DB.Create(&thing)

	thing2 := Thing{

//
//	type User struct {
//	  Toys []Toy `gorm:"polymorphic:Owner;"`
//	}
//	type Pet struct {
//	  Toy Toy `gorm:"polymorphic:Owner;"`
//	}
//	type Toy struct {
//	  OwnerID   int
//	  OwnerType string
//	}
func (schema *Schema) buildPolymorphicRelation(relation *Relationship, field *Field) {
	polymorphic := field.TagSettings["POLYMORPHIC"]

	relation.Polymorphic = &Polymorphic{

		}
	case schema.Many2Many:
		joinModel := reflect.New(rel.JoinTable.ModelType).Interface()
		joinDB := base.Session(&Session{NewDB: true, Context: ctx}).Model(joinModel)

		// EXISTS owners: owners.pk = join.owner_fk for all owner refs
		ownersExists := base.Session(&Session{NewDB: true, Context: ctx}).Table(rel.Schema.Table).Select("1")
		for _, ref := range rel.References {
			if ref.OwnPrimaryKey && ref.PrimaryKey != nil {

For example, if you have an app like this:

```Python
from fastapi import FastAPI
from pydantic import BaseModel

class Item(BaseModel):
    name: str
    price: Optional[float] = None
    owner_ids: Optional[List[int]] = None

app = FastAPI()

@app.get("/items/invalidnone", response_model=Item)
def get_invalid_none():
    return None
```