[Bugfix]: correctly propagate errors message caught at the chat_templating step to the client (vllm-project#18769)

Signed-off-by: Guillaume Calmettes <[email protected]>

Author: gcalmettes

vllm/entrypoints/chat_utils.py

@@ -1252,7 +1252,7 @@ def apply_hf_chat_template(
         # investigation.
         logger.exception(
             "An error occurred in `transformers` while applying chat template")
-        raise ValueError from e
+        raise ValueError(str(e)) from e
 
 def apply_mistral_chat_template(
     tokenizer: MistralTokenizer,
@@ -1281,7 +1281,7 @@ def apply_mistral_chat_template(
     # We convert those assertion errors to ValueErrors so they can be
     # are properly caught in the preprocessing_input step
     except (AssertionError, MistralCommonException) as e:
-        raise ValueError from e
+        raise ValueError(str(e)) from e
 
     # External library exceptions can sometimes occur despite the framework's
     # internal exception management capabilities.
@@ -1292,7 +1292,7 @@ def apply_mistral_chat_template(
         logger.exception(
             "An error occurred in `mistral_common` while applying chat "
             "template")
-        raise ValueError from e
+        raise ValueError(str(e)) from e
 
 def random_tool_call_id() -> str:
     return f"chatcmpl-tool-{random_uuid()}"