check content (Azure#23496)

Author: xiangyan99

sdk/identity/azure-identity/CHANGELOG.md

@@ -8,6 +8,8 @@
 
 ### Bugs Fixed
 
+- Added check on `content` from msal response    ([#23483](https://github.com/Azure/azure-sdk-for-python/issues/23483))
+
 ### Other Changes
 
 ## 1.9.0b1 (2022-03-08)

sdk/identity/azure-identity/azure/identity/_internal/msal_client.py

@@ -52,7 +52,9 @@ def raise_for_status(self):
 
         if ContentDecodePolicy.CONTEXT_NAME in self._response.context:
             content = self._response.context[ContentDecodePolicy.CONTEXT_NAME]
-            if "error" in content or "error_description" in content:
+            if not content:
+                message = "Unexpected response from Azure Active Directory"
+            elif "error" in content or "error_description" in content:
                 message = "Authentication failed: {}".format(content.get("error_description") or content.get("error"))
             else:
                 for secret in ("access_token", "refresh_token"):