diff --git a/ldp/alg/optimizer/ape.py b/ldp/alg/optimizer/ape.py
index de0529a..5d25a52 100644
--- a/ldp/alg/optimizer/ape.py
+++ b/ldp/alg/optimizer/ape.py
@@ -196,7 +196,7 @@ def aggregate_trajectory(self, trajectory: Trajectory) -> None:
                 # m is a Message with a result of the LLM. Which completes only strings.
                 # and we checked the result exists above.
                 x = next(
-                    cast(str, m.content) 
+                    cast(str, m.content)
                     for m in result.prompt
                     if (isinstance(m, Message) and m.role == "user")
                 )