Pass None for empty password

tests/test_handler.py

@@ -83,3 +83,5 @@ class TestIndexHandler(unittest.TestCase):
         with self.assertRaises(InvalidValueError) as exc:
             pkey = IndexHandler.get_pkey_obj('x'+key, password, fname)
             self.assertIn('Invalid private key', str(exc))
+        with self.assertRaises(paramiko.PasswordRequiredException):
+            pkey = IndexHandler.get_pkey_obj(key, '', fname)

webssh/handler.py

@@ -118,7 +118,7 @@ class IndexHandler(MixinHandler, tornado.web.RequestHandler):
 
     @classmethod
     def get_pkey_obj(cls, privatekey, password, filename):
-        bpass = to_bytes(password)
+        bpass = to_bytes(password) if password else None
 
         pkey = cls.get_specific_pkey(paramiko.RSAKey, privatekey, bpass)\
             or cls.get_specific_pkey(paramiko.DSSKey, privatekey, bpass)\