The following change looks good to me:

-        if isinstance(address, str):
+        if isinstance(address, (str, bytes)):
             self.unixsocket = True
             self._connect_unixsocket(address)

But I don't understand the testcase. Is an address starting with a NULL character a special address? How does it the bytes address case?

+        # override the definition in the base class
+        self.address = '\x00python_logging_test'

"syslog logging handler fails with address in unix abstract namespace"

What is the unix abstract namespace?