Default to None for unix_socket option

Author: takluyver

docs/source/server-process.rst

@@ -114,8 +114,6 @@ pairs.
     this path and listen for HTTP requests on it. The ``port`` configuration key
     will be ignored.
 
-    Defaults to *False*.
-
 
 ``mappath``
 ^^^^^^^^^^^

jupyter_server_proxy/config.py

@@ -118,7 +118,7 @@ def make_server_process(name, server_process_config, serverproxy_config):
         timeout=server_process_config.get('timeout', 5),
         absolute_url=server_process_config.get('absolute_url', False),
         port=server_process_config.get('port', 0),
-        unix_socket=server_process_config.get('unix_socket', False),
+        unix_socket=server_process_config.get('unix_socket', None),
         mappath=server_process_config.get('mappath', {}),
         launcher_entry=LauncherEntry(
             enabled=le.get('enabled', True),