What is the ruling when an offer to free a slave is conditional upon marrying a daughter?

Primary text

If a person states, 'Free your slave on the condition that I marry your daughter to you,' and the owner frees the slave, the promisor is not obligated to marry his daughter to the offeror. This arrangement is deemed a loan (salam) concerning the marriage contract. The promisor owes the monetary value of the slave to the person who freed him. The basis for this ruling is that the property (the slave) was alienated based on a stipulated compensation; therefore, the compensation is obligatory, analogous to stating, 'Free your slave for me, and I owe you its price,' or 'Divorce your wife, and I owe you a thousand,' upon which the divorce would obligate payment.