There is no reason to not assume that status:null isn't 'M'.

tests/rietveld_test.py

 #!/usr/bin/env python
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Unit tests for rietveld.py."""
 
 import logging
 import os
 import sys
@@ skipping 70 matching lines @@
       self.assertEquals(p.is_git_diff, is_git_diff)
     self.assertEquals(p.is_new, is_new)
     if hasattr(p, 'patchlevel'):
       self.assertEquals(p.patchlevel, patchlevel)
     if diff:
       self.assertEquals(p.get(True), diff)
     if hasattr(p, 'svn_properties'):
       self.assertEquals(p.svn_properties, svn_properties)
 
   def test_get_patch_no_status(self):
-    self.requests = [('/api/123/456', _api({'file_a': {}}))]
-    try:
-      self.rietveld.get_patch(123, 456)
-      self.fail()
-    except patch.UnsupportedPatchFormat, e:
-      self.assertEquals('file_a', e.filename)
+    self.requests = [
+        ( '/api/123/456',
+          _api(
+            {
+              'tools/clang_check/README.chromium': {
+                'status': None,
+                'id': 789,
+              }})),
+        ('/download/issue123_456_789.diff', RAW.DELETE),
+    ]
+    patches = self.rietveld.get_patch(123, 456)
+    self.assertEquals(1, len(patches.patches))
+    self._check_patch(
+        patches.patches[0],
+        'tools/clang_check/README.chromium',
+        RAW.DELETE,
+        is_delete=True)
 
   def test_get_patch_2_files(self):
     self.requests = [
         ('/api/123/456',
           _api({'foo': _file('A'), 'file_a': _file('M', chunk_id=790)})),
         ('/download/issue123_456_789.diff', RAW.NEW),
         ('/download/issue123_456_790.diff', RAW.NEW_NOT_NULL),
     ]
     patches = self.rietveld.get_patch(123, 456)
     self.assertEquals(2, len(patches.patches))
@@ skipping 262 matching lines @@
     ]
     for i in self.rietveld.search(base='base'):
       self.assertEquals(expected.pop(0), i)
     self.assertEquals([], expected)
 
 
 if __name__ == '__main__':
   logging.basicConfig(level=[
     logging.ERROR, logging.INFO, logging.DEBUG][min(2, sys.argv.count('-v'))])
   unittest.main()