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

Primary text

If the master specifies 'one of my female slaves,' the heirs are prohibited from entering into a contract of manumission with a male slave (ʿabd) or an intersex person whose sex is indeterminate (khunthā mushkal) for the same reason of uncertainty regarding their status.