make sure that client info is not None

Author: Noravee

src/mcp/client/auth/extensions/client_credentials.py

@@ -88,6 +88,10 @@ async def _perform_authorization(self) -> httpx.Request:
 
     async def _exchange_token_client_credentials(self) -> httpx.Request:
         """Build token exchange request for client_credentials grant."""
+
+        if not self.context.client_info or not self.context.client_info.client_id:
+            raise OAuthTokenError("No client info available")  # pragma: no cover
+
         token_data: dict[str, Any] = {
             "grant_type": "client_credentials",
             "client_id": self.context.client_info.client_id,