better handling since xgen tokenizer breaks with convert_tokens_to_ids

src/axolotl/prompt_tokenizers.py

@@ -48,16 +48,22 @@ class PromptTokenizingStrategy(abc.ABC):
 
     @functools.lru_cache(maxsize=128)
     def _get_user_token(self):
-        id_or_ids = self.tokenizer.convert_tokens_to_ids("<|USER|>")
-        if isinstance(id_or_ids, (int,)):
-            return id_or_ids
+        try:
+            id_or_ids = self.tokenizer.convert_tokens_to_ids("<|USER|>")
+            if isinstance(id_or_ids, (int,)):
+                return id_or_ids
+        except KeyError:
+            pass
         return False
 
     @functools.lru_cache(maxsize=128)
     def _get_assistant_token(self):
-        id_or_ids = self.tokenizer.convert_tokens_to_ids("<|ASSISTANT|>")
-        if isinstance(id_or_ids, (int,)):
-            return id_or_ids
+        try:
+            id_or_ids = self.tokenizer.convert_tokens_to_ids("<|ASSISTANT|>")
+            if isinstance(id_or_ids, (int,)):
+                return id_or_ids
+        except KeyError:
+            pass
         return False
 
     def _tokenize(self, prompt: str, add_eos_token=True, strip_bos_token=False):