Convert None logits processor/stopping criteria to empty list. (#19880)

* Convert None logits processor/stopping criteria to empty list.

* Initialize stopping_criteria, logits_processor in generate.

* Default stopping_criteria, logits_processor to None.
Co-authored-by: Chandler May <chandler.j.may@gmail.com>

src/transformers/generation_utils.py

@@ -997,9 +997,9 @@ class GenerationMixin:
         num_beam_groups: Optional[int] = None,
         diversity_penalty: Optional[float] = None,
         prefix_allowed_tokens_fn: Optional[Callable[[int, torch.Tensor], List[int]]] = None,
-        logits_processor: Optional[LogitsProcessorList] = LogitsProcessorList(),
+        logits_processor: Optional[LogitsProcessorList] = None,
         renormalize_logits: Optional[bool] = None,
-        stopping_criteria: Optional[StoppingCriteriaList] = StoppingCriteriaList(),
+        stopping_criteria: Optional[StoppingCriteriaList] = None,
         constraints: Optional[List[Constraint]] = None,
         output_attentions: Optional[bool] = None,
         output_hidden_states: Optional[bool] = None,
@@ -1277,6 +1277,8 @@ class GenerationMixin:
         num_return_sequences = (
             num_return_sequences if num_return_sequences is not None else self.config.num_return_sequences
         )
+        logits_processor = logits_processor if logits_processor is not None else LogitsProcessorList()
+        stopping_criteria = stopping_criteria if stopping_criteria is not None else StoppingCriteriaList()
 
         pad_token_id = pad_token_id if pad_token_id is not None else self.config.pad_token_id
         eos_token_id = eos_token_id if eos_token_id is not None else self.config.eos_token_id