Merge pull request #5 from charles-dyfis-net/issues/4

UTF-8 encode passwd only when set (fixes: #4)

ldappool/__init__.py

@@ -139,6 +139,7 @@ class ConnectionManager(object):
         return len(self._pool)
 
     def _match(self, bind, passwd):
+        if passwd is not None:
             passwd = passwd.encode('utf8')
         with self._pool_lock:
             inactives = []
@@ -200,6 +201,7 @@ class ConnectionManager(object):
         """
         tries = 0
         connected = False
+        if passwd is not None:
             passwd = passwd.encode('utf8')
         exc = None
         conn = None