f a $1$:M relationship is optional on both sides, which of the following is true?

The resulting foreign key can have null $($empty$)$ values

The resulting foreign key cannot have null $($empty$)$ values

The resulting foreign key must have null $($empty$)$ values

No foreign key is created as a result of mapping such a relationship

Two foreign keys are created as a result of mapping such a relationship, one that can have null $($empty values$)$ and one that cannot have null $($empty values$)$