diff --git a/aider/utils.py b/aider/utils.py
index 3daa2d734..f69c953bf 100644
--- a/aider/utils.py
+++ b/aider/utils.py
@@ -86,7 +86,9 @@ def replace_part_with_missing_leading_whitespace(whole, part, replace):
         )
 
         if matched:
-            replace_lines = [leading_whitespace + rline for rline in replace_lines]
+            replace_lines = [
+                leading_whitespace + rline if rline else rline for rline in replace_lines
+            ]
             whole_lines = whole_lines[:i] + replace_lines + whole_lines[i + len(part_lines) :]
             return "\n".join(whole_lines) + "\n"