diff --git a/lmms_eval/api/task.py b/lmms_eval/api/task.py
index ddf817485..6dd32ec66 100755
--- a/lmms_eval/api/task.py
+++ b/lmms_eval/api/task.py
@@ -1577,9 +1577,9 @@ def construct_requests(self, doc_id: int, ctx: str, **kwargs) -> Union[List[Inst
     def process_results(self, doc, results, full_docs=None):
         if self.OUTPUT_TYPE in ("generate_until", "generate_visual_cot"):
             if isinstance(results, list) and isinstance(results[0], list):
-                results = [res.strip() for res in results[0]]
+                results = [res.strip() if res is not None else "" for res in results[0]]
             else:
-                results = [res.strip() for res in results]
+                results = [res.strip() if res is not None else "" for res in results]
 
         kwargs = {}
         if full_docs is not None:
@@ -1664,7 +1664,7 @@ def process_results(self, doc, results, full_docs=None):
 
         elif "generate_until" in self.OUTPUT_TYPE:
             gold = self.doc_to_target(doc)
-            result = [res.strip() for res in results]
+            result = [res.strip() if res is not None else "" for res in results]
             if self.config.doc_to_choice is not None:
                 # If you set doc_to_choice,
                 # it assumes that doc_to_target returns a number.