Many to Many assosiation fails due to invalid bulk-returning query

[BidyadharM]

When there's a Many-to-Many relationship, the Bulk returning into query, doesn't take into account the conflict resolution between an inserted and non inserted record.

Test Name: TestNestedManyToManyPreload3

Description:

type (
		Level1 struct {
			ID    uint
			Value string
		}
		Level2 struct {
			ID      uint
			L2Value string
			Level1s []*Level1 `gorm:"many2many:level1_level2;"`
		}
		Level3 struct {
			ID       uint
			L3Value  string
			Level2ID sql.NullInt64
			Level2   *Level2
		}
	)

	if err := DB.AutoMigrate(&Level3{}, &Level2{}, &Level1{}); err != nil {
		t.Error(err)
	}

	level1Zh := &Level1{Value: "zh"}
	level1Ru := &Level1{Value: "ru"}
	level1En := &Level1{Value: "en"}

	level21 := &Level2{
		L2Value: "Level2-1",
		Level1s: []*Level1{level1Zh, level1Ru, level1En},
	}

	level22 := &Level2{
		L2Value: "Level2-2",
		Level1s: []*Level1{level1Zh, level1En},
	}

	wants := []*Level3{
		{
			L3Value: "Level3-1",
			Level2:  level21,
		},
		{
			L3Value: "Level3-2",
			Level2:  level22,
		},
		{
			L3Value: "Level3-3",
			Level2:  level21,
		},
	}
        if err := DB.Save(wants[0]).Error; err != nil {
		t.Error(err)
	}

        if err := DB.Save(wants[1]).Error; err != nil {
		t.Error(err)
	}

        if err := DB.Save(wants[2]).Error; err != nil {
		t.Error(err)
	}

During the call DB.Save(wants[1]), the merge -query generated in invalid.