diff --git a/aider/coders/wholefile_coder.py b/aider/coders/wholefile_coder.py
index a3766559f..6028bf3c5 100644
--- a/aider/coders/wholefile_coder.py
+++ b/aider/coders/wholefile_coder.py
@@ -127,15 +127,16 @@ class WholeFileCoder(Coder):
 
     def do_live_diff(self, full_path, new_lines, final):
         if Path(full_path).exists():
-            orig_lines = self.io.read_text(full_path).splitlines(keepends=True)
+            orig_lines = self.io.read_text(full_path)
+            if orig_lines is not None:
+                orig_lines = orig_lines.splitlines(keepends=True)
 
-            show_diff = diffs.diff_partial_update(
-                orig_lines,
-                new_lines,
-                final=final,
-            ).splitlines()
-            output = show_diff
-        else:
-            output = ["```"] + new_lines + ["```"]
+                show_diff = diffs.diff_partial_update(
+                    orig_lines,
+                    new_lines,
+                    final=final,
+                ).splitlines()
+                return show_diff
 
+        output = ["```"] + new_lines + ["```"]
         return output