Minor compatibility fix: support None as argument for iter_tree_contents.

dulwich/object_store.py

@@ -1648,7 +1648,7 @@ def _collect_ancestors(
 
 
 def iter_tree_contents(
-        store: ObjectContainer, tree_id: bytes, *, include_trees: bool = False):
+        store: ObjectContainer, tree_id: Optional[ObjectID], *, include_trees: bool = False):
     """Iterate the contents of a tree and all subtrees.
 
     Iteration is depth-first pre-order, as in e.g. os.walk.
@@ -1659,6 +1659,8 @@ def iter_tree_contents(
     Returns: Iterator over TreeEntry namedtuples for all the objects in a
         tree.
     """
+    if tree_id is None:
+        return
     # This could be fairly easily generalized to >2 trees if we find a use
     # case.
     todo = [TreeEntry(b"", stat.S_IFDIR, tree_id)]

dulwich/tests/test_object_store.py

@@ -223,6 +223,7 @@ class ObjectStoreTests:
             [TreeEntry(p, m, h) for (p, h, m) in blobs],
             list(iter_tree_contents(self.store, tree_id)),
         )
+        self.assertEqual([], list(iter_tree_contents(self.store, None)))
 
     def test_iter_tree_contents_include_trees(self):
         blob_a = make_object(Blob, data=b"a")