fix(diff): mode-assertions now deal with 0

If the file was not present, the mode seen in a diff can be legally '0',
which previously caused an assertion to fail for no good reason.
Now the assertion tests for None instead.

Closes #323

1 files changed, 2 insertions, 2 deletions

diff --git a/git/diff.py b/git/diff.py
index dc53f3f7..9059091e 100644
--- a/git/diff.py
+++ b/git/diff.py
@@ -223,12 +223,12 @@ class Diff(object):
         if a_blob_id is None:
             self.a_blob = None
         else:
-            assert self.a_mode
+            assert self.a_mode is not None
             self.a_blob = Blob(repo, hex_to_bin(a_blob_id), mode=self.a_mode, path=a_path)
         if b_blob_id is None:
             self.b_blob = None
         else:
-            assert self.b_mode
+            assert self.b_mode is not None
             self.b_blob = Blob(repo, hex_to_bin(b_blob_id), mode=self.b_mode, path=b_path)
 
         self.new_file = new_file