What is the ruling on stipulating the release of the mortgage on both slaves upon paying the debt associated with only one partner's share?

Primary text

If one partner stipulates that upon paying his portion of the debt, the mortgage on the slave he pledged, and the mortgage on the other partner's share in the second slave, should be released, this stipulation is void (*fasid*). This is because it stipulates the release of a mortgage securing one debt by paying a different debt. The entire mortgage (*rahn*) becomes void because this condition imposes a defect or detriment upon the creditor (mortgagee). Any void condition that diminishes the right of the mortgagee invalidates the mortgage.