Cause: Multipath wasn't blacklisting tapdev, which cannot be multipathed. It tried to multipath them, but their sysfs format is different from expected path devices.
Consequence: Multipathd could crash if multiple tadpdev devices were removed from the system.
Fix: Multipath now blacklists /dev/td[a-z].* device by default.
Result: Multipath will no longer try to setup multipath devices on tapdev devices, and will not crash when they are removed.