{Core} aaz: Fix MgmtErrorFormat missing message from response (#32927)

Author: necusjz

src/azure-cli-core/azure/cli/core/aaz/_error_format.py

@@ -133,7 +133,7 @@ def __init__(self, json_object):
         # ARM specific annotations
         self.additional_info = [
             TypedErrorInfo(additional_info["type"], additional_info["info"])
-            for additional_info in self.get_object_prop(json_object, self.ADDITIONALINFO_LABEL, [])
+            for additional_info in self.get_object_prop(json_object, self.ADDITIONALINFO_LABEL, []) or []
         ]
 
     def __str__(self):

src/azure-cli-core/azure/cli/core/tests/test_aaz_error_format.py

@@ -0,0 +1,21 @@
+# --------------------------------------------------------------------------------------------
+# Copyright (c) Microsoft Corporation. All rights reserved.
+# Licensed under the MIT License. See License.txt in the project root for license information.
+# --------------------------------------------------------------------------------------------
+import unittest
+
+from azure.cli.core.aaz._error_format import AAZMgmtErrorFormat
+
+
+class TestMgmtErrorFormat(unittest.TestCase):
+    def test_additional_info_is_null(self):
+        response = {
+            "code": "BadRequest",
+            "message": "Test.",
+            "target": None,
+            "details": None,
+            "additionalInfo": None
+        }
+
+        error = AAZMgmtErrorFormat(response)
+        self.assertTrue(str(error) == '(BadRequest) Test.\nCode: BadRequest\nMessage: Test.')