[clang-format] A Minor change to clang-format-diff.py

Summary: Testing for None should use the 'is' operator.

Reviewed By: MyDeveloperDay

Patch By:  eagleoflqj

Tags: #clang-format

Differential Revision: https://reviews.llvm.org/D77974

clang/tools/clang-format/clang-format-diff.py

@@ -65,7 +65,7 @@ def main():
     match = re.search(r'^\+\+\+\ (.*?/){%s}(\S*)' % args.p, line)
     if match:
       filename = match.group(2)
-    if filename == None:
+    if filename is None:
       continue
 
     if args.regex is not None: