[fix]解决单测test_encode报错问题

vllm/engine/llm_engine.py

@@ -989,14 +989,15 @@ class LLMEngine:
                 output = [outputs_by_sequence_group[0][i]]
 
             # tree style speculative decoding may generate empty output in first step
-            samples = [o.samples[0] for o in output]
-            valid_samples = [
-                sample for sample in samples
-                if sample.output_token != VLLM_INVALID_TOKEN_ID
-            ]
-            if len(valid_samples) == 0:
-                empty_seq_indices.append(i)
-                continue
+            if outputs and isinstance(output[0], SamplerOutput):
+                samples = [o.samples[0] for o in output]
+                valid_samples = [
+                    sample for sample in samples
+                    if sample.output_token != VLLM_INVALID_TOKEN_ID
+                ]
+                if len(valid_samples) == 0:
+                    empty_seq_indices.append(i)
+                    continue
 
             if not is_async:
                 seq_group.update_num_computed_tokens(