What is the ruling regarding a Mukatab's contract upon his death based on the opinion of Imam Malik?

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Imam Malik holds that if the Mukatab has a free child, the contract of manumission is nullified. Furthermore, if the Mukatab possesses a slave within his ownership under the contract, the master is compelled to enforce the payment of the entire remaining sum if the deceased had wealth. If he possessed no wealth, the master is compelled to force the heirs to work and pay the outstanding amount.