ip_address only accepts unicode on Python 2

ipaddress.ip_address('127.0.0.1') fails with ValueError on Python 2

need to decode it, otherwise 127.0.0.1 won't be treated as local

jupyter_server/base/handlers.py

@@ -35,7 +35,7 @@
 
 from traitlets.config import Application
 from ipython_genutils.path import filefind
-from ipython_genutils.py3compat import string_types
+from ipython_genutils.py3compat import string_types, PY3
 
 import jupyter_server
 from jupyter_server._tz import utcnow
@@ -419,6 +419,10 @@ def check_host(self):
         if host.startswith('[') and host.endswith(']'):
             host = host[1:-1]
 
+        if not PY3:
+            # ip_address only accepts unicode on Python 2
+            host = host.decode('utf8', 'replace')
+
         try:
             addr = ipaddress.ip_address(host)
         except ValueError: