Just return empty lists instead of None

bin/mechanicaldiff.py

@@ -6,7 +6,7 @@ import sys
 
 def filter_change_block(
     change_lines: list[str], search: str, replace: str
-) -> list[str] | None:
+) -> list[str]:
     removed_lines = []
     added_lines = []
     phase = "minus"
@@ -31,7 +31,7 @@ def filter_change_block(
         return change_lines
 
     if len(removed_lines) != len(added_lines):
-        return None
+        return []
 
     kept_lines = []
     for removed, added in zip(removed_lines, added_lines):
@@ -42,16 +42,16 @@ def filter_change_block(
             kept_lines.append(f" {removed}")
 
     if not kept_lines:
-        return None
+        return []
 
     return kept_lines
 
 
 def filter_hunk(
     hunk_lines: list[str], search: str, replace: str
-) -> list[str] | None:
+) -> list[str]:
     if not hunk_lines:
-        return None, False
+        return []
 
     header = hunk_lines[0]
     body = hunk_lines[1:]
@@ -73,7 +73,7 @@ def filter_hunk(
         i += 1
 
     if not any(line.startswith(("+", "-")) for line in output_body):
-        return None
+        return []
 
     return [header] + output_body
 
@@ -120,12 +120,10 @@ def main() -> None:
         kept_hunks = []
         for hunk_lines in section["hunks"]:
             filtered = filter_hunk(hunk_lines, search, replace)
-            if filtered:
             if filtered != hunk_lines:
                 left_out = True
+            if filtered:
                 kept_hunks.append(filtered)
-            elif hunk_lines:
-                left_out = True
 
         if not kept_hunks:
             left_out = True