Fix the same bug in content_understanding_client

Author: Zhi Zhou

python/content_understanding_client.py

@@ -27,9 +27,10 @@ def __init__(
         self._endpoint = endpoint.rstrip("/")
         self._api_version = api_version
         self._logger = logging.getLogger(__name__)
-        self._headers = self._get_headers(
-            subscription_key, token_provider(), x_ms_useragent
-        )
+
+        token = token_provider() if token_provider else None
+
+        self._headers = self._get_headers(subscription_key, token, x_ms_useragent)
 
     def _get_analyzer_url(self, endpoint, api_version, analyzer_id):
         return f"{endpoint}/contentunderstanding/analyzers/{analyzer_id}?api-version={api_version}"  # noqa