check for None value in utils.safe_header

In case that a sensetive header (that should be obscured by its SHA1
hash) is None, the safe_header throws an exception which fails the
calling process and by that may harm the functionality.

Change-Id: I56944a382fd546eba0a6dd6d6b1cecf83b1dc106
Closes-Bug: #1491311

glanceclient/tests/unit/test_utils.py

@@ -177,3 +177,18 @@ class TestUtils(testtools.TestCase):
         i = utils.IterableWithLength(data, 10)
         self.assertRaises(IOError, _iterate, i)
         data.close.assert_called_with()
+
+    def test_safe_header(self):
+        self.assertEqual(('somekey', 'somevalue'),
+                         utils.safe_header('somekey', 'somevalue'))
+        self.assertEqual(('somekey', None),
+                         utils.safe_header('somekey', None))
+
+        for sensitive_header in utils.SENSITIVE_HEADERS:
+            (name, value) = utils.safe_header(sensitive_header, 'somestring')
+            self.assertEqual(sensitive_header, name)
+            self.assertTrue(value.startswith("{SHA1}"))
+
+            (name, value) = utils.safe_header(sensitive_header, None)
+            self.assertEqual(sensitive_header, name)
+            self.assertIsNone(value)