diff --git a/trl/trainer/grpo_trainer.py b/trl/trainer/grpo_trainer.py
index e15585dd3e1..dd605750a0e 100644
--- a/trl/trainer/grpo_trainer.py
+++ b/trl/trainer/grpo_trainer.py
@@ -1705,8 +1705,22 @@ def _generate_and_score_completions(
     ) -> dict[str, torch.Tensor | Any]:
         device = self.accelerator.device
         mode = "train" if self.model.training else "eval"
-
-        prompts = [x["prompt"] for x in inputs]
+        
+        def remove_empty_fields(data):
+            if isinstance(data, dict):
+                return {k: remove_empty_fields(v) for k, v in data.items() if v is not None}
+            elif isinstance(data, list):
+                return [remove_empty_fields(item) for item in data if item is not None]
+            else:
+                return data
+
+        prompts = []
+        cleaned_inputs = []
+        for item in inputs:
+            cleaned_item = remove_empty_fields(item)
+            cleaned_inputs.append(cleaned_item)
+            prompts.append(cleaned_item["prompt"])
+        inputs = cleaned_inputs
 
         if self.environments:
             for prompt, environment, reset_kwargs in zip(prompts, self.environments, inputs, strict=True):