Fix minor bug from PR #325 (#330)

* Fix issue #118

* Fix error when self._known_host_file is None and None is passed to load_host_keys

* Update test_sftp.py

storages/backends/sftpstorage.py

@@ -58,7 +58,8 @@ def _connect(self):
         )
 
         if os.path.exists(known_host_file):
-            self._ssh.load_host_keys(self._known_host_file)
+            self._ssh.load_host_keys(known_host_file)
+
 
         # and automatically add new host keys for hosts we haven't seen before.
         self._ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())

tests/test_sftp.py

@@ -1,9 +1,12 @@
+import os
 import stat
 from datetime import datetime
+
 try:
     from unittest.mock import patch, MagicMock
 except ImportError:  # Python 3.2 and below
     from mock import patch, MagicMock
+
 from django.test import TestCase
 from django.core.files.base import File
 from django.utils.six import BytesIO
@@ -23,6 +26,13 @@ def test_no_known_hosts_file(self, mock_ssh):
         self.storage._connect()
         self.assertEqual('foo', mock_ssh.return_value.connect.call_args[0][0])
 
+    @patch.object(os.path, "expanduser", return_value="/path/to/known_hosts")
+    @patch.object(os.path, "exists", return_value=True)
+    @patch('paramiko.SSHClient')
+    def test_error_when_known_hosts_file_not_defined(self, mock_ssh, *a):
+        self.storage._connect()
+        self.storage._ssh.load_host_keys.assert_called_once_with("/path/to/known_hosts")
+
     @patch('paramiko.SSHClient')
     def test_connect(self, mock_ssh):
         self.storage._connect()