openai[patch]: add check for none values when summing token usage (#27585)

**Description:** Fixes None addition issues when an empty value is
passed on

If no one reviews your PR within a few days, please @-mention one of
baskaryan, efriis, eyurtsev, ccurme, vbarda, hwchase17.

libs/partners/openai/langchain_openai/chat_models/base.py

@@ -605,6 +605,8 @@ class BaseChatOpenAI(BaseChatModel):
             token_usage = output["token_usage"]
             if token_usage is not None:
                 for k, v in token_usage.items():
+                    if v is None:
+                        continue
                     if k in overall_token_usage:
                         overall_token_usage[k] = _update_token_usage(
                             overall_token_usage[k], v