If a deceased master states, 'Enter into a contract of manumission with one of my male slaves (ʿabīdī),' and he also owned female slaves, who may the heirs choose?

Primary text

If the master specifies 'one of my male slaves,' the heirs may select one of them. However, the heirs are prohibited from entering into a contract of manumission with a female slave (amah) or an intersex person whose sex is indeterminate (khunthā mushkal), because the status of the latter as either a male slave or a female slave cannot be ascertained.