Fix type issues

dulwich/client.py

@@ -1699,7 +1699,7 @@ class SubprocessGitClient(TraditionalGitClient):
     def from_parsedurl(cls, parsedurl, **kwargs):
         return cls(**kwargs)
 
-    git_command = None
+    git_command: Optional[str] = None
 
     def _connect(
         self,

dulwich/diff_tree.py

@@ -46,7 +46,7 @@ _NULL_ENTRY = TreeEntry(None, None, None)
 _MAX_SCORE = 100
 RENAME_THRESHOLD = 60
 MAX_FILES = 200
-REWRITE_THRESHOLD = None
+REWRITE_THRESHOLD: Optional[int] = None
 
 
 class TreeChange(namedtuple("TreeChange", ["type", "old", "new"])):