Don't crash when header is value of None

Before commit 7d88d14d (http://git.io/hhJWdQ) swifclient used to accept
header value with the type None :

{'Headers': None}

It would just be happy with it with those None headers and not process
them, reinstate the old behavior.

Closes-Bug: 1256441
Change-Id: Ic7f80c38ef2ce9ef1687ed0d6d65521f2e754905

swiftclient/client.py

@@ -97,7 +97,9 @@ def quote(value, safe='/'):
 
 def validate_headers(headers):
     if headers:
-        for key, value in headers.iteritems():
+        for key, raw_value in headers.iteritems():
+            value = str(encode_utf8(raw_value))
+
             if '\n' in value:
                 raise InvalidHeadersException("%r header contained a "
                                               "newline" % key)

tests/test_swiftclient.py

@@ -190,6 +190,11 @@ class TestHttpHelpers(MockHttpTest):
         self.assertRaises(c.InvalidHeadersException, c.validate_headers,
                           headers)
 
+    def test_validate_headers_with_other_than_str(self):
+        for t in (None, 1, 1.0, 1L, u"A"):
+            self.assertEqual(c.validate_headers({'key': t}),
+                             None)
+
 # TODO: following tests are placeholders, need more tests, better coverage