fix copies

src/transformers/models/whisper/tokenization_whisper_fast.py

@@ -584,9 +584,15 @@ def get_prompt_ids(self, text: str, return_tensors="np"):
 
     # Copied from transformers.models.whisper.tokenization_whisper.WhisperTokenizer._strip_prompt
     def _strip_prompt(self, token_ids: List[int], prompt_token_id: int, decoder_start_token_id: int):
-        has_prompt = isinstance(token_ids, list) and token_ids and token_ids[0] == prompt_token_id
         if not isinstance(token_ids, list):
             token_ids = self._convert_to_list(token_ids)
+
+        # handle case of empty token_ids for decoding with timestamps.
+        # at this point token_ids is a list, so it is safe to use if not check.
+        if not token_ids:
+            return token_ids
+
+        has_prompt = token_ids[0] == prompt_token_id
         if has_prompt:
             if decoder_start_token_id in token_ids:
                 return token_ids[token_ids.index(decoder_start_token_id) :]